Signedon plaque: 1-1-1- / AMPERE SHUNT / FOR / WESTON STANDARD / MILLI-VOLTMETER N93155 / MADE BY THE / WESTON ELECTRICAL INSTRUMENT CO / NEWARK. N.J. US.A.
FunctionShunts like this one are used to divert the electric current measured by a meter, in order to protect it and extend its range. This particular one has three ranges, either 0.1, 1 or 10 Amps, depending on which binding posts are connected.
The plate indicates that it was for Weston Standard Milli-Voltmeter.