Usage : To find extensive use as a DC null detector in wheat stone bridges and potentiometers.

Light source: 6 volt and 0.3 Amp. bulb.

Scale :is 150 mm long and is marked for both Center and end zero use.

Zero set: the spot of  light can be set  at any point on the scale.

Sensitivity Control: is controlled by a two pole, 6 way switch  The switch positions are D, 1/10, 1/100, 1/1000 and s/c.