This circuit was found in a Popular Electronics from the 90's. Its purpose is to detect the ionization of the air. The meter can be replaced by the current scale of an ordinary multimeter.
Maxim MAX20094 and MAX20095 Battery Chargers Maxim Integrated offers through Mouser Electronics high...
This circuit suggested by Intersil, provides a Kelvin scale of 3 and a half digits in a 7106, with...
Found in National Semiconductor documentation from the 1990s, this circuit switches video signals to...