PURPOSE: To virtually eliminate magnetic influence even in monitoring with an easy azimuth adjustment without causing individual difference by indicating the direction of deviation in the (x) axis of a magnetic detector with the lighting of one of multiple lamps and the degree of the deviation on the brightness thereof.
CONSTITUTION: A y-axis magnetic signal outputted from a magnetic detector 2 varies in the polarity depending on the direction of the deviation in the (x) axis. The polarity is discriminated with a polarity discriminator 7, with which the common contact 10a of a changeover switch 10 is turned to the individual contact 10b or 10c corresponding to the polarity. For example, when the (x) axis of the magnetic detector 2 is deviated in the north-west, the output in the Y axis is positive and hence, the common contact 10a of the changeover switch 10 is connected to one individual contact 10b. Therefore, as a multiplier 8 conducts to one incandescent lamp 11 to light it. To the contrary, when the (x) axis is deviated in the north-east, the output in the Y axis is negative, and with the polarity discriminator 7, the common contact 10a of the changeover switch 10 is connected to the other individual contact 10c to light the other incandescent lamp 12.
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