It has a range from 0 to 150 Volts. There are no markings on the switches or the jumper wire to indicate what they do. We need to disassemble the device determine how it works.
Hoyt A. C. Volts 0-150 Meter, the 348 Type 531
This A.C. Volt Meter was made by Hoyt Electrical Instrument Works in Penacook, New Hampshire.