Signedstamped on top: O. Wolff Berlin / 2718 / Manganin
Inscribedinscribed in oval plate with eagle image: PTR. 93*[star]. / 1900;
inscribed on top: 0.01 int. Ohm / bei. 20°C
Functionfor suspension in mercury to a standard bridge set in an oil bath.
A 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 orifice on top is to insert a thermometer, which is not present. A hard rubber cap would usually cover this orifice (see other resistance standards).