Signedon top of wooden case: HARTMANN & BRAUN / FRANKFURT A.M. / No.4528
Inscribedstamped into side of hard rubber panel: 1 Ohm = 106,3 cm/mm² Hg. 0°C
stamped on top of rubber panel, inside rectangle of blocks: Richtig bei 20°C
resistances marked: 1000, 10000, 10000, [infinity] 30000
FunctionSuch an instrument is used to control the resistance of electric conductors. For a short general description and other images, go to the following website.
The series of brass blocks are connected to one another with the coils underneath. When the plugs are all in, the resistance is negligible. When one or more plugs are removed, the resistance of that or these plugs are introduced into the electric current passing through the box.