Maker's Name: 
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20.5 × 12 × 13 cm

An instrument for measuring ground resistance. It uses three electrodes, spaced at least 20 m apart in a straight line. The first is the test ground, the middle one is the auxiliary voltage ground and the third is the auxiliary current ground.

A mechanical vibrator operating from a nominal 3.6 V DC at 108 Hz +/-4% supplies a bridge with AC. One arm is variable and reads from 0 to 50. Another arm selects the range x0.1R, x1R, x10R, x100R. The AC current is fed to the end electrodes and the potential difference is measred between the first and middle electrodes.  The resistances in the bridge are adjusted until the meter shows a null, when the setting of the variable arm multiplied by the range figure gives the ground resistance.

The tester is run by a 4.5V torch battery.