Electrostatic voltmeters (electrometers)

Physikfan, Sun Oct 09 2016, 08:44AM

Here is a picture of an electrostatic voltmeter (electrometer) for a maximum of 250 V.



I have two questions:

Please, who has electrostatic voltmeters, recognizable by the capacitor symbol with the arrow.
And please, who has experience with such instruments as well as with the performance?