FOR PROVIDING REFERENCE PLANES

TECHNICAL FIELD

[0001] The present subject matter is related, in general, to a laser leveling device for provid ing reference planes and, in particular, to methods for verification of working of such laser leveling devices.

BACKGROUND

[0002] Conventionally, a laser leveling device for providing reference planes is configured to produce a horizontal and/or vertical laser beam(s) for providing a horizontal reference laser plane and/or a vertical reference laser plane. Such laser leveling devices are used for ind icating level, plumb, and square in construction field as well as in other scientific and technical fields for which the prerequisites include marking of horizontal and vertical planes. However, it is necessary to verify at regular intervals the working of such a laser leveling device in order to ascertain whether the reference plane provided by the laser leveling device is actually horizontal or vertical for accurately ind icating level or for accurately ind icating plumb and square, respectively.

BRIEF DESCRIPTION OF THE DRAW INGS

[0003] The detailed description is described with reference to the accompanying figures. I n the figures, the left- most d igit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the d rawings to reference like features and components.

[0004] Figure l a illustrates an example of a verification system for verifying horizontalness or verticalness of a laser beam prod uced by a laser leveling device, accord ing to one embod iment of the present subject matter. [0005] Figure lb illustrates an example of a verification system for verifying horizontalness or verticalness of a laser beam produced by a laser leveling device, according to another embodiment of the present subject matter.

[0006] Figure 2 illustrates an example of a stand for holding tubes vertically, in a verification system according to an embodiment of the present subject matter.

[0007] Figures 3a and 3b illustrate a distance measuring device provided on a tube, in a verification system according to an embodiment of the present subject matter. [0008] Figures 4a and 4b illustrate a practical use of verifying horizontalness or verticalness of a laser beam produced by a laser leveling device, according to an embodiment of the present subject matter.

[0009] Figure 5 illustrates an example of a flowchart of a method for verifying horizontalness and/or verticalness of a laser beam produced by a laser leveling device, according to an embodiment of the present subject matter.

[0010] Those skilled in the art will appreciate that figures herein represent conceptual views for verifying horizontalness or verticalness of a laser beam produced by a laser leveling device, embodying application of the principles of the present subject matter.

DETAILED DESCRIPTION f 0011] The present subject matter is directed towards verifying functionality of a laser leveling device that provides a horizontal and/or vertical reference plane. The horizontal or vertical reference plane may be required for accurately measuring horizontalness or verticalness of any structure using the laser leveling device.

|0012] The laser leveling device may include a laser diode, a collimator, and an optical system, wherein ihe laser diode emits a laser beam, and the collimator converts the laser beam into a coilimated laser beam. Further, the optical system divides the col!imated beam into output beams having a perpendicular relationship with each other. Of which, the first laser beam provides horizontal reference plane, and the second laser beam provides the vertical reference plane. Here, the first laser beam is parallel with a horizontal plane, and the second laser beam is perpendicular to the horizontal plane. Here, the horizontal plane can be defined as a plane tangent to the earth's surface at an observer's position.

[0013] Conventionally, the verification of the laser leveling device is performed indoor in a controlled environment. Otherwise, various environmental factors like temperature, humidity, etc., adversely affect the verification. Accordingly, outdoor or on-site verification is generally not preferred as it may give erroneous results. For example, on-site verification of the horizontalness of a 10 meter long laser beam may involve an error of, say + 10%, as compared to the error of, say +1%, for the verification done in a controlled environment, such as at the factory by the skilled workers. However, the verification in the factory involves extra cost and loss of time in logistics. Moreover, it is a recurring cost and delay as the verification is required on a regular basis to meet international standards.

[0014] One more problem in conventional verification techniques is that the verification of horizontalness or verticalness of long distance laser beams may not be possible indoor due to limited space. If the verification of horizontalness or verticalness of the long distance laser beams is performed outdoor, then an error in the verification can be quite high due to uncontrollable environmental factors. In one method, the verification of horizontalness or verticalness of the long distance laser beams is performed indoor in a controlled environment at a reduced scale, i.e.. using a relatively short distance laser beam. In said method, verification readings taken for the relatively short distance laser beam are proportionally exaggerated with respect to the long distance laser beam. However, verification error is also exaggerated proportionally in said method while exaggerating the verification readings. For example, horizontalness of a 100 meter long laser beam produced by a laser leveling device needs to be verified. In said examp le, the laser leveling device can be sent to a factory for the sake of the controlled environment. In the factory, the laser leveling device produces, say, a 10 meter long laser beam. The horizontalness of said 10 meter long laser beam is verified in the factory with an error of, say, +1 %. Therefore, horizontalness of 100 meter long laser beam if it is verified in the factory may be exaggerated to an error of + 10%. Accord ingly, verification of horizontalness or verticalness of long distance laser beams within a min imum error limit is a challenge.

[0015] To this end, the present subject matter first describes outdoor or on- site verification of horizontalness of a long d istance laser beam produced by a laser leveling device. The present subject matter is based on the principle that a surface of a liquid, such as water, forms horizontal plane irrespective of whatever is the size of its surface. S imilarly if the water is stored in d liferent containers and if the containers are interconnected, i.e., are in fluid connection with each other, the water surface in each container is in the same horizontal plane as that of the water surface in other containers.

[0016] For the purpose of the verification of the laser leveling device, a minimum of three tubes partially fil led with a liquid, such as water, may be used to define a plane. Each tube should be transparent and should have one end open. In one example, three burettes may be used instead of transparent tubes. These tubes or burettes may be p laced on the ground or any uneven surface at any desired distance from each other. In one example, the d istance ma be as large as possible which is within a working range of the laser leveling device. In one example, the desired d istance can be up 1 50 to 200 meters. The tubes are held vertically on the ground or uneven surface, with the he lp of respective stands. The tubes may be in fluid connection with each other by means of p ipes so that the surface of water in each of the tubes is in the same horizontal plane. In one example, the tubes, along with the ir stands, may be p laced at an angle of about 120 degree with each other in a horizonta l p lane. [0017] A laser leveling device, for example, a rotary laser leveling device, is operated such that its first laser beam sequentially produces a first laser spot one after another on the tubes or on a vertical screen provided adjacent to each of the tubes. At the same time, the position of the first laser spot may be marked in the tubes or on the vertical screen. A distance measuring device that can be provided on the tubes is used to measure the distance between the marked first laser spot and the liquid level for each of the tubes. The d istance measuring device may be a scale with a least count of a millimeter or a depth micrometer with a least count of a micrometer. After measuring the distance between the surface of the liquid and the marked first laser spot of the first laser beam for each of the tubes, deviations between the measured d istances are determined. For this purpose, each of the measured distances is compared with each of all the other measured distances. If the there is no deviation between the measured distances, it means that the first laser beam is perfectly horizontal and the laser leveling device is determined fit for use, such as measuring horizontalness of a structure. However, if there are deviations between the measured d istances, a maximum deviation between is determined by ded ucting maximum distance from the minimum distance of the measured d istances. The maximum deviation is then compared with a first threshold value, say of, +3 mm. The first threshold value may be predefined. If the maximum deviation is within the first threshold value, it is determined that the first laser beam is acceptably horizontal and the laser leveling device is fit for use, such as for measuring horizontalness of a structure. If the maximum deviation exceeds the first thresho ld value, it is determined that the first laser beam is not horizontal and the laser leveling device is not fit for the use.

[0018] In a similar manner, vertica lness of a second laser beam can also be verified. For this purpose, a laser leveling device of rotary type can be used. Such a laser leveling device simultaneously prod uces a first laser beam and a second laser beam which are substantially perpend icular with each other. The first laser beam may be horizontal and the second laser beam may be vertical in normal use. Any manuiacturing defect or post-manufacturing fault may d isturb the angle between two beams and the beams may not remain perpend icular with each other. Such a d isturbance or deviation from the perpend icular relationship between two beams may be verified using the present subject matter. Once the horizontalness of the first laser beam is verified as described above, a path of a second laser spot formed on a horizontal screen by the second laser beam can be observed by rotatably operating the laser leveling device in a horizontal plane about a rotationa l axis of the laser leveling device. For example, if the second laser beam is substantially perpendicular to the first laser beam, the position of the second laser spot formed by the second laser beam will not change during rotation of the laser leveling device in the horizontal plane. However, if the second laser spot formed by the second laser beam defines a circular path d uring rotation of the laser leveling device in the horizontal p lane, then a rad ius of the circular path can be compared with a second threshold va lue, which may be predefined. If the rad ius of the circular path is less than the second thresho ld value, then the second laser beam can be determined acceptab ly vertical and the laser leveling device can be determined fit for use, such as measuring verticalness of a structure. Further, the first laser beam and the second laser beam can be determined at right angle with each other. On the other hand, if the measured d istance is greater than the second thresho ld value, the second laser beam can be determined non-vertical and the laser leve ling d evice can be determined unfit for the use. Further, the first laser beam and the second la ser beam can be determined to be at an angle other than the right angle with each other.

[0019] The verification o f ho rizo nta lness or vertica lness of laser beams produced by a laser leveling device as per the p resent subject matte r does not require contro lled environment o f the factory and, therefore, can be performed on-s ite or outdoor without compromis ing on accuracy o f verification. I n fact, accuracy can be achieved within a least co unt o f a mil limeter or micrometer, e ven for long d istance laser beams, suc h as 1 20 meter long laser beams. F urthermore, the verification is simple and does not require expensive tools, therefore, can be done by a non-skilled person, thus substantial cost and time can be saved.

[0020] The aspects defined above and further aspects of the present subject matter are apparent from the example of embodiments to be described hereinafter and are explained with reference to the figures. The present subject matter will be described in more detail hereinafter with reference to the exemplary embodiments, but to which the present subject matter is not limited.

[0021] Figure la illustrates a verification system 100 for verifying horizontalness of a first laser beam produced by a laser leveling device 102, according to an embodiment of present subject matter. The horizontalness of the first laser beam means whether the first laser beam produced by the laser leveling device 102 is in the horizontal plane. Here, the horizontal plane can be defined as a plane tangent to the earth's surface at an observer's position. In this embodiment, the verification system 100 comprises at least three tubes 104, namely a first tube, a second tube, and a third tube, which are held vertically and individually by using a stand 106 for each of them to form a polygon. In one implementation, the three tubes 104 may be preferably placed at an angle of about 120 degree approximately from each other to form an equilateral triangle. The laser leveling device 102 may be positioned inside of the polygonal or triangular arrangement of the tubes 104. The three tubes 104 may be in fluid connection with each other using pipes 108, for example, PVC pipes, and a coupler 110 which connects the pipes 108 with each other. In this context, the term "fluid connection" means that a liquid can freely flow from one tube to the other tubes. In one example, a first end of a first pipe 108 is connected to bottom portion of the first tube 104 and a second end of the first pipe 108 is coupled to a coupler 110. Similarly, a first end ofthe second pipe 108 is connected to bottom portion of the second tube and a second end of the second pipe 108 is coupled to the coupler I 10. Similarly, a first end of the third pipe 108 is connected to the bottom portion ofthe third tube and a second end ofthe third pipe 108 is coupled to the coupler 110. Further, a liquid, such as water, is filled in the tubes 104.. In one implementation, the tubes 104 may be of a transparent material, such as glass, so that the liquid level in the tubes 104 is visible from outside to an observer. The water remains at a same level in all the tubes 104 due to the principle that a surface of a liquid, such as water, forms horizontal plane irrespective of whatever is the size of its surface. Similarly if the water is stored in different containers and if the containers are interconnected using a fluid connection, the water surface in each container is in the same horizontal plane as that of the surfaces in other containers. Further, the pipes 108 may be of a flexible material so that they can be easily laid down for long distances on an uneven territory.

[0022] In operation, when the laser leveling device 102, such as a rotary laser leveling device, is rotatably operated, the laser leveling device 102 produces a first laser beam which is expected to be horizontal; however, it is to be verified whether it is actually horizontal. The first laser beam produces a first laser spot one after another on the tubes 104 or on a vertical screen (not shown) provided adjacent to each of the tubes 104. A distance measuring device (not shown) that can be provided on the tubes 104 is used to measure the distance between the first laser spot and the liquid level for each of the tubes 104. Further, a maximum deviation between the measured distances for each of the tubes 104 is determined. For this purpose, each of the measured distances is compared with all other measured distances to find out a minimum distance and a maximum distance from amongst the measured distances. Then, the minimum distance is deducted from the maximum distance to determine the maximum deviation between the measured distances. If the there is no deviation between the measured distances, it is determined that the first laser beam is horizontal and the laser leveling device 102 is fit for use, such as measuring horizontalness of a structure. If there are deviations between the measured distances, the- maximum deviation is compared with a first threshold value, say + 3 mm, which may be predetermined. If the maximum deviation is less than the first threshold value, then the laser leveling device 102 is determined fit for use, such as measuring horizontalness of a structure, as the first laser beam is acceptab ly horizontal. If the maximum deviation is greater than the first thresho ld value, then the laser leveling device 102 can be determined unfit for the use as the first laser beam is not horizontal. [0023] As illustrated in Figure l b, more than three tubes 104 may also be utilized as per requirement, such as the site of verification or line of sight. As shown, an arrangement of four tubes 104 may be utilized for the purpose of verification of the horizontalness or verticalness of laser beam(s) produced by a laser leveling device 102. As shown in the figure l b, three tubes 104 may be preferably placed at an angle of about 120 degree from each other in order and fourth tube 104 may be placed in the center of the arrangement. In one example, a distance between the fourth tube 104 at the center and each of said three tubes 104 is, say 60 meters. A vertical screen 1 12 may be provided adjacent to one or more of the tubes 104 for the purpose of receiving the first laser beam from the laser leveling device 102.

[0024] Table 1 given below illustrates exemp lary read ings for two laser leveling devices having serial no. 001241 and 001040 which may be verified using a verification system shown in Figure l b. I n one examp le, two read ings are taken for each ofthe laser leveling devices.

001040 21 mm 22 mm 21 mm 23 mm 2 mm

32 mm 33 mm 34 mm 32 mm 2 mm

Table -1

[0025] In case of laser leveling device having serial no.001241, in the first set of readings, the distance observed/measured between the first laser spot and liquid level is 21 mm for each tube. Since maximum deviation between the measured distances is 0 mm, therefore, the laser leveling device having serial no. 001241 is producing a first laser beam which is perfectly horizontal. In the second set of readings, the distance observed/measured between the first laser spot and liquid level is 31 mm for each tube. Since maximum deviation between the measured distances is again 0 mm, therefore the verification results of first reading are verified by the second reading. Accordingly, the laser leveling device having serial no. 001241 can be determined fit for use, such as measuring horizontalness of a structure.

[0026] In case of laser leveling device having serial no.001040, in the first set of reading, the distance observed/measured between the first laser spot and liquid level is 21 mm, 22 mm, 21 mm, and 23 mm for the four tubes, respectively. Since maximum deviation between the measured distances is 2 mm, therefore, the laser leveling device having serial no.001040 is producing a first laser beam which is acceptably horizontal as the maximum deviation is less than a first threshold value of, say, +3 mm. In second set of readings, the distance observed/measured between the first laser spot and liquid level is 32 mm, 33 mm, 34 mm, and 32 mm for the four tubes respectively. Since maximum deviation between the measured distances is again 2 mm, therefore the verification results of first reading are verified by the second reading. Accordingly, the laser leveling device 102 having serial no. 001040 can be determined fit for use, such as measuring horizontalness of a structure. [0027] Figure 2 illustrates how the stand 106 holds the tube 104 vertically, in the verification system 100 according to an embodiment of the present subject matter. The stand 106 comprises a horizontal plate 202 and a vertical rod 204 mounted on the horizontal plate 202. One or more clamps 206 are fitted to the vertical rod 204. The one or more clamps 206 hold the tube 104 such that the tube 104 is vertical. This arrangement of the stand 106 and the tube 104 can be placed in an uneven territory at long distances from other similar arrangements to form a polygon. Further, the laser leveling device 102 may be positioned inside the polygon.

[0028] Figures 3a and 3b illustrate a distance measuring device 302, 304 provided on the tubes 104, according to an embodiment of the present subject matter. The distance measuring device 302, 304 is provided on the tubes 104 for measuring a distance between a first laser spot 310 and the liquid level in each of the tubes 104. In first example, the distance measuring device 302, 304 can be a scale 302 for measuring the d istance at millimeter level as depicted in Figure 3a. The sca le 302 may be an external scale or printed on the transparent material of the tubes 104. Further, the scale 302 may be provided inside or outside of the tubes 104 such that the d istance between the first laser spot 310 and the liquid level can be measured. In second examp le, the d istance measuring device 302, 304 can be a depth micrometer 304 for measuring the d istance at micrometer level as depicted in Figure 3b. The depth micrometer 304 may be provided on the top portion of the tubes 104 such than a base plate of the micrometer 304 rests on the top portion of the tube 104. However, if the length of the base plate of the depth micrometer 304 is less than d iameter of the tube 104 or otherwise also, a glass plate 306 having a hole 308 in its centre and having sufficient d imensions may be kept/fitted on the top portion of the tube 104 such that a rod of the depth micrometer 304 passes through the ho le 308 for the purpose of measuring distance between the first laser spot 31 0 and the liq uid leve l.

[0029] Figure 4a and 4b illustrate on-s ite verification o horizontaJness and/or vertica lness of a first laser beam and/or a second laser bea m prod uced by a laser leveling device, according to an embod iment of the present subject matter. At the site, a tower 402 is being erected. As shown, the tower 402 is erected on a foundation 404, which is laid on the ground 406. In one example, the tower 402 may be of a wind turbine and can be as high as 100 to 200 meters. Laser leveling devices, such as the laser leveling device 102 can be used to provide a reference horizontal or vertical plane during construction/erection of the tower 402. The laser leveling device 102 may be a rotary laser leveling device that can be rotatably operated in a horizontal plane about a rotational axis of the laser leveling device 102. The laser leveling device 102 can be used to measure horizontalness or verticalness of the tower 402 by checking whether any two or more points on the tower 402 are in a horizontal line or in a vertical line. Before that, it has to be verified whether the laser leveling device 102 is actually fit for use or not. Otherwise, any error caused by unverified laser leveling device may result into construction/erection of a tower that is inclined to vertical plane.

[0030] For the purpose of verification of the laser leveling device 102, at least three tubes 104, namely a first tube, a second tube, and a third tube along with a stand 106 for each of the tube can be placed on the ground 406 near the tower 402. The tubes can be placed at a desired d istance (D) from each other to form a polygon. The desired d istance may be as long as it is allowed by working range of the laser leveling device 102, which may be positioned inside the polygon. In one example, the desired d istance (D) may be up to 150 to 200 meters. A bottom portion of the tubes 104 may be coup led with each other through pipes 108 and an optional coupler. A liq uid, such as water, may be poured in the tubes 104 such that the liquid is at a same level in the tubes 104 due to atmospheric pressure. The laser leveling device 102 may be rotatab ly operated to d irect a first laser beam on the tubes 104. The first laser beam forms a first laser spot on the tubes 104 or a see-through vertical screen (not shown) near the tubes 104. A d istance (H I , H2) between the first laser spot and the liq uid leve l can be measured at each of the tubes 104. Further, each o f the measured d istances (H I , H2) may be compared with each ofa ll the other measured d istances (H I , H2) to determine a maximum deviation between the measured distances (HI, H2). If the maximum deviation is zero, then the laser leveling device 102 can be determined fit for measuring horizontalness as the first laser beam is perfectly horizontal. However, if the maximum deviation is non-zero, then the maximum deviation can be compared with a first threshold value, which may be predetermined. If the maximum deviation is less than the first threshold value, then the laser leveling device 102 can be determined fit for measuring horizontalness as the first laser beam is acceptably horizontal. On the other hand, if the maximum deviation is greater than the first threshold value, then the laser leveling device 102 can be determined unfit for measuring horizontalness as the first laser beam is not horizontal.

[0031] In one implementation, the laser leveling device 102 can also be used for verifying verticalness of a second laser beam. For this purpose, the laser leveling device 102 can be of rotary type, which simultaneously emits two laser beams at a theoretical angle of 90 degrees between the first laser beam and the second laser beam. This type of the laser leveling device 102 can be first used to verify horizontalness of the first laser beam as explained above and then to verify verticalness of the second laser beam. Once horizontalness of the first laser beam is verified, the verticalness of the second laser beam is automatically verified assuming the manufacturing of laser leveling device 102 is correct and there is no post-manufacturing fault in the laser leveling device 102 that may have changed the theoretical angle. However, when there is such a manufacturing delect or post-manufacturing fault, the same can also be verified using the verification system 100. For this purpose, a horizontal screen 408 can be provided for receiving the second laser beam. As illustrated in Figures 4a and 4b, the horizontal screen 408 can be mounted to the top of the tower 402 such that it ^• extends horizontally outward from the top of the tower 402 and is above the laser leveling device 102. When the laser leveling device 102 is operated the second laser beam forms a second laser spot 410 on the horizontal screen 408. [0032] When the laser leveling device 102 is slightly moved about the rotational axis, the position of the second laser spot 410 on the horizontal screen 408 changes if the second laser beam is not perfectly vertical or is not at a perfect right angle to the first laser beam. Similarly, the position ofthe second laser spot 410 will not change if the second laser beam is perfectly vertical, and if the second laser beam and the rotational axis of the laser leveling device 102 are in the same line. It is to be noted here that the position ofthe second laser spot 410 can also change while the laser leveling device 102 is being slightly moved due to a horizontal offset or distance between the rotational axis and the second laser beam. Therefore, the second laser beam should originate at a point on the rotational axis of the laser leveling device 102 for the purpose of verification of verticalness of the second laser beam or verification of the right angle between the first laser beam and the second laser beam.

[0033] In one example, when the laser leveling device 102 is rotated say through 360 degrees in a horizontal plane about a rotational axis of the laser leveling device 102, a pattern formed by the second laser spot 410 on the horizontal screen 408 may be observed. If the second laser beam is perfectly vertical, the second laser spot 410 will define a dot on the horizontal screen 408 while the laser leveling device 102 is being rotated. It is therefore determined that the second laser beam is at a perfect right angle to the first laser beam. Further, the laser leveling device 102 can be determined fit for measuring verticalness of a structure.

[ ^' 0034] On the other hand, if the second laser beam is not perfectly vertical, the second laser spot410 defnesa circular path 12 on the horizontal screen 408 while the laser leveling device 102 is being rotated. The circular path 412 has a radius ( ) that depends on the error or deviation ofthe second laser beam with reference to the rotational axis. The radius (M) of the circular path 412 may be measured and compared with a second threshold value, such as +_3 mm. If the radius ofthe circular path 412 is less than the second threshold value, then the laser leveling device 102 can be determined to be producing acceptably vertical laser beam as the angle between the first laser beam and the second laser beam is nearly right angle. If the radius of the circular path 412 is greater than the second threshold value, then the laser leveling device 102 can be determined unfit for measuring verticalness of a structure as the angle between the first laser beam and the second laser beam is not right angle.

[0035] Figure 5 illustrates a flowchart of a method 500 for verification of horizontainess of a first laser beam produced by a laser leveling device 102. This method 500 can be used for outdoor or on-site verification of horizontainess of the first laser beam produced by the laser leveling device 102. The first laser beam may be as long as allowed by working range of the laser leveling device 102.

[0036] Firstly, at step 502, various components required for forming a verification system 100 are brought to the site. In one example, the required components include three or more tubes 104, stands 106 for the tubes 104, pipes 108 and a coupler 110 for connecting the tubes 104, a vertical screen 112 (optional), and a distance measuring device 320, 304.

[0037] At step 504, the components are assembled on-site to form the verification system 100. In the verification system 100, the tubes 104 are held vertically using the stands 106 at a desired distance from each other to form a polygon. Further, the laser leveling device 102 may be positioned inside the polygonal arrangement of the tubes 104. Further, a bottom portion of the tubes 104 is coupled with corresponding first end of pipes 108. Second end of pipes 108 are coupled with each other using the coupler 110, such as a coupler 110 having three or more pins depending upon number of pipes 108 to be coupled to the coupler 110.

[0038] Further, a liquid, such as water, is partially filled in the tubes 104 such that the partially filled liquid is at a same horizontal level within each of the tubes 104. The tubes 104 are in fluid connection with each other. In this context, the term "fluid connection" means that the liquid can freely flow from one tube 104 to the other tubes 104. in one implementation, the tubes 104 may be of a transparent material, such as glass, so that the liquid level in the tubes 104 is visible from outside to an observer.

[0039] Further, vertical screens 112 may be optionally provided adjacent to one or more of the tubes 104 for receiving a first laser beam from the laser leveling device 102. Otherwise, the first laser beam may be received on the tubes 104. Accordingly, the first laser beam forms a first laser spot on the vertical screen 112 or the tubes 104. The distance measuring device 302, 304, can be mounted on the tubes 104 for measuring a distance between liquid level and the first laser spot for each of the tubes 104.

[0040] At step 506, the laser leveling device 102 is rotatably operated to sequentially direct a first laser beam onto the vertical screens 112 or the tubes 104 one by one. In one example, a platform on which the laser leveling device 102 is kept that can be rotated. Otherwise, the laser leveling device 102 of rotary type may be preferably used for this purpose.

[0041] At step 508, position of the first laser spot formed due to the first laser beam is marked on the vertical screen 112 or the tubes 104. In one example, an observer may manually mark the position of the first laser spot.

[0042] At step 10, a distance between liquid level and the marked position of the first laser spot is measured for each of the tubes 104 to obtain a plurality of measured distances. The distance measuring device 302, 304 can be used for measuring the distance at each of the tubes 104. The distance measuring device 302, 304 may be a scale 302 for taking millimeter level measurements or a depth micrometer 304 for taking micrometer level measurements.

[0043] At step 512. each of the plurality of measured distances is compared with each of all the other measured distances to determine a maximum deviation between the plurality of measured distances. In one implementation, the maximum deviation between the measured d istances can be measured manually or through a computing system. In order to determine the maximum deviation between the plurality o f measured d istances, a minimum d istance from amongst the plurality of measured d istances is deducted from a maximum d istance from amongst the p lura lity o f measured distances.

[0044] At step 514, the maximum deviation compared with a first thresho ld value for determining whether the laser leveling device 102 is fit or unfit for use, such measuring horizontalness of a structure.

[0045] At step 516, the laser leveling device 102 is determined fit or unfit for use based on the comparison o f the maximum deviation with the first threshold value. More specifically, the laser leveling device 1 02 is determined fit if the maximum deviation is zero or less than the first threshold value as it means that the first laser beam is perfectly or acceptably horizontal. Further, the laser leveling device is determined unfit for use if the maximum deviation is greater than the first threshold value as the first laser beam is cannot be accepted to be horizonta l.

[0046] In one imp lementation, the method 500 can be extended to verify vertica lness o f a second laser beam emitted by a laser leveling device, such as the laser leveling device 1 02. For this purpose, the laser leveling d evice can be of rotary type, which s imultaneously emits two laser beams at a theoretica l angle of 90 degrees between the laser beams. Of which, the first lase r beam is horizontal and the second laser beam is vertica l. This type of the laser leve ling dev ice can be first used to verify horizonta lness o f the first laser beam as exp lained above. Once horizonta lness of the first laser beam is verified at the step 5 1 6, the vert ica lness o f the second laser beam is automatica lly verified assuming the manufacturing of laser leveling device is correct and there is no post- manufac turing fault in the laser leve ling de vice that may have changed the theoretica l angle. However, when there is such a manufacturing defect or post- manufacturing fau lt, the same can a lso be verified us ing the verification system. For this purpose, the second laser beam from the laser leveling device can be directed on a horizontal screen where it forms a second laser spot.

[0047] When the laser leveling device is slightly moved about the rotational axis, the position of the second laser spot on the horizontal screen changes if the second laser beam is not perfectly vertical or is not at a perfect right angle to the first laser beam. Similarly, the position of the second laser spot will not change if the second laser beam is perfectly vertical, and if the second laser beam and the rotational axis of the laser leveling device are in the same line. It is to be noted here that the position of the second laser spot can also change while the laser leveling device is being slightly moved due to a horizontal offset or distance between the rotational axis and second laser beam. Therefore, the second laser beam should originate at a point on the rotational axis of the laser leveling device for the purpose of verification of verticalness of the second laser beam or verification of the right angle between the first laser beam and the second laser beam.

[0048] In one example, when the laser leveling device is rotated say through 360 degrees in a horizontal plane about a rotational axis of the laser leveling device, a pattern or path formed by the second laser spot on the horizontal screen may be traced. If the second laser beam is perfectly vertical, the second laser spot will define a dot on the horizontal screen while the laser leveling device is being rotated in the horizontal plane. It is therefore determined that the second laser beam is at a perfect right angle to the first laser beam. Further, the laser leveling device can be determined fit for measuring verticalness of a structure.

[0049] On the other hand, if the second laser beam is not perfectly vertical, the second laser spot defines a circular path on the horizontal screen while the laser leveling device is being rotated in the horizontal plane. The circular path has a radius that depends on the error or deviation of the second laser beam with reference to the rotational axis. The radius of the circular path may be measured and compared with a second threshold value, such as +_3 mm. If the radius of the circular path is less than the second threshold va lue, then the laser leveling d evice can be determined to be producing acceptab ly vertical laser beam as the angle between the first laser beam and the second laser beam is nearly right angle. If the rad ius of the c irc ular path is greater than the second thresho ld value, then the laser leveling device can be determined unfit for measuring verticalness of a structure as the angle between the first laser beam and the second laser beam is not right angle.

[0050] The d ifferent embod iments provided above are not limiting and are only illustrative examp les of the d ifferent scope of the present subject matter. Other imp lementations apparent to a person sk illed in the art are also included within the scope of the present subject matter.