voltmeter vintage with wooden cover

50s accuracy alternating ammeter ampere amperemeter analog ancient antique cables cage carefully check circle circuit conductivity conductor control danger device dial display door electric electrician electrocution electronic energy engineering equipment examination experience experiment flash frame gauge generator handle handworker house indicators industrial industry inspect instrument job measure measurement meter metric monitor needle numbers old power proof retro safety scale tesla test time tool tools used verify vintage volt voltage voltmeter wires wooden work worker workman