Signedstamped on top: O. Wolff Berlin 2710
Inscribedon top in an elliptical metal marker: PTR 256 [above an eagle] / 1903 [below the eagle]
on the top: 4 int Ohm / bei 20°C / Manganin
FunctionA resistance standard is not to measure the resistance of an electric conductor but rather to compare such a conductor to a temperature-fixed resistance. In other words, such a device is used to determine the value of an unknown current. To do so, a current in the conductor would pass through mercury (for the older type of standard resistance), into which the two leads from the resistor dip. The manganin wire in this instrument was baked before being dipped into paraffin so that all moisture is removed and to improve the insulation over the wire.
ProvenanceFrom the Department of Physics, Jefferson Laboratory, Harvard University.