Measuring wheel instruments are well known in the art. A measuring wheel of known dimensions is rolled along, usually manually by means of a handle attached to either the wheel or a housing. Each rotation of the measuring wheel thus corresponds to a known distance. By pushing the wheel along and counting the number of rotations, the linear distance travelled can be measured.

A counter mechanism can be attached to the wheel to register the number of rotations. The counter mechanism can be either mechanical, as shown in US 3716919, or electronic, as shown in US 4176458. The mechanism usually includes a display to indicate the distance travelled, either as an indication of the number of wheel rotations (which can be interpreted as a distance by the user) or as an actual distance. The display can be digital or analogue, and usually has means to reset it.

It is desirable for the measuring wheel in such instruments to have a large diameter because the error in distance measurements increases with the number of rotations. Thus, a larger measuring wheel means fewer rotations for the same distance, therefore less error on

that distance. However, large wheels are cumbersome and difficult to transport.

With the advent of more precise machinery, smaller measuring wheels can be produced without prejudicing the accuracy of the instruments. However, smaller wheels are harder for the operator to control, especially when the surface to be measured is uneven.

At its most general, the present invention provides a relatively small balancing wheel to stabilise a measuring wheel instrument, to give the operator more control. The balancing wheel may be small enough to be moulded in one piece so that a through shaft, or indeed any connection with the measuring wheel is not necessary.

Of course, a smaller wheel requires less material, and if a through shaft is not required, then the apparatus has fewer components. This saves manufacturing costs.

According to the present invention, there is provided a distance measuring apparatus having: a measuring wheel; a counter to record rotation of the measuring wheel, the counter being located in a housing; a handle for pushing the measuring wheel along a surface; and a balancing wheel to stabilise the apparatus ; wherein the balancing wheel has a diameter smaller than the diameter of the measuring wheel.

Preferably, the balancing wheel is independently rotatable. Preferably, the diameter of the balancing wheel is less than one half, or more preferably less than one quarter, of the diameter of the measuring wheel.

Preferably, the balancing wheel is axially spaced from the measuring wheel, i. e. the balancing means may be provided adjacent the measuring wheel rather than behind or in front of it. Preferably, the balancing wheel contacts the surface when the measuring wheel is being pushed along it. Preferably, the balancing wheel is not coaxial with the measuring wheel.

Preferably, the counter is in mechanical connection with the measuring wheel.

Preferably, the measuring wheel is located in but protrudes from the housing. Preferably, it protrudes from the housing by less than 2 cm; more preferably it protrudes from the housing by less than 1 cm.

Preferably, the balancing wheel is located in but protrudes from the housing. It may be moulded in a single piece with an integral axle which may be received by corresponding slots in the housing.

Preferably, the counter has a display for indicating the distance travelled by the measuring wheel. The display may have means to reset it. Preferably, the means reset the display to zero.

Preferably, the handle is length-adjustable.

Preferably, the handle is a plurality of coaxial tubes threaded into each other, such that the length of the handle is adjustable by sliding the tubes relative to one another. The tubes may be secured relative to each other by twisting.

An embodiment of the invention will now be described in more detail with reference to the accompanying drawings, in which: Fig. 1 shows a perspective view of a measuring wheel instrument which is an embodiment of the invention; Fig. 2 shows a front view of the measuring wheel instrument. of Fig. 1; Fig. 3 shows a rear view of the measuring wheel instrument of Fig. 1; Fig. 4 shows a view looking down on the measuring wheel instrument of Fig. 1 ; Fig. 5 shows a first side view of the measuring wheel instrument of Fig. 1; Fig. 6 shows a second side view of the measuring wheel instrument of Fig. 1 ; Fig. 7 shows a view from below the measuring wheel instrument of Fig. 1 ; Fig. 8 shows a side view of the measuring wheel instrument of Fig. 1 with the handle partially extended;

Fig. 9 shows a side view of the measuring wheel instrument of Fig. 1 with the handle fully extended.

Fig. 1 shows a measuring wheel instrument 1 which is an embodiment of the present invention. It comprises protective housing 3, which is made of e. g. two parts 3a, 3b of durable material (e. g. engineering plastics) fixed together e. g. by screws or welding using attachment pegs 30 (see Fig. 5), and handle 2 which is fixed in between parts 3a, 3b of housing 3 so that it extends away from it.

Fig. 2 shows measuring wheel 4 located at one side of housing 3 and mostly enclosed by it. The measuring wheel 4 rotates on an axle about an axis created by the joining together of parts 3a, 3b. The rest of housing 3 contains a gear counter mechanism (not shown) connected to measuring wheel 4 to record the amount that measuring wheel 4 rotates. Gear mechanisms of this type (e. g. involute or convolute) are well known in the art.

Measuring wheel 4 protrudes slightly from the base of housing 3 so that it can engage with a surface.

Fig. 3 shows hollow 9 formed in the base of housing 3 at the other side to measuring wheel 4. Jockey wheel 5 is located in hollow 9. Jockey wheel 5 is formed in e. g. one piece with an integral axle 10 which sits in axle holes formed in parts 3b, 3c, thereby being rotatably

fixed in place when parts 3b, 3c are attached together.

Jockey wheel 5 has a smaller diameter than measuring wheel 4, but is positioned so that it will engage a surface at the same time as measuring wheel 4, thereby giving better stability to the measuring wheel instrument 1 because there are two spaced points of contact with the surface rather than only one. This makes it easier to maintain the measuring wheel 4 at the correct orientation.

The circumference of the measuring wheel 4 is e. g. approximately 12 inches; the circumference of the jockey wheel 5 is e. g. approximately 3 inches.

On the top of housing 3, there is a display window 7, through which a display 11 of the gear counter mechanism can be seen. Display 11 can be a set of rotating dials which indicate the distance travelled, or any other known means of identifying the distance measured.

In Fig. 6, a reset lever 6 is provided outside the housing 3 for resetting the display 11 to e. g. zero.

Figs. 8 and 9 show different configurations of the extensible handle arrangement. Handle 2 may include e. g. three coaxial sections 12 of increasing diameter which are threaded inside one another in a telescopic-type arrangement. The outermost coaxial section 12 has a hand

grip 8 at the end furthest from the housing 3. The end of the innermost coaxial section 12 closest to housing 3 is attached to the housing as explained above. The middle and outermost coaxial sections 12 have screw grips 21 located at their end that are respectively closest to the housing 3. The screw grips 21 and coaxial section are of irregular cross section, so that by twisting the screw grip 21, they either loosen or tighten their hold on the coaxial section 12 on which they are threaded. Thus, the length of the handle 2 may be varied by loosening a screw grip 21, passing a required length of coaxial section 12 past it before tightening it.

The described embodiment is provided by way of example only it it will be appreciated by a person skilled in the art that the invention can be achieved in ways other than those specifically described.