Calibration device for electrical instruemnts having an error percentage indicator

Claim 1

A TEST CIRCUIT FOR CALIBRATING AN ELECTRIC INSTRUMENT, COMPRISING: A VARIABLE SOURCE OF VOLTAGE; CIRCUIT OUTPUT TERMINALS FOR CONNECTING SAID INSTRUMENT THERETO; FIRST CIRCUIT MEANS CONNECTING SAID SOURCE OF VOLTAGE TO SAID TERMINALS FOR APPLYING A VOLTAGE THERETO; A RESISTANCE DECADE IN CIRCUIT WITH SAID VARIABLE VOLTAGE SOURCE; SWITCH MEANS FOR SETTING SAID DECADE TO VARIOUS RESISTANCES; SECOND CIRCUIT MEANS CONNECTED TO SAID RESISTANCE DECADE TO TAKE OFF A STANDARD VOLTAGE RELATED IN MAGNITUDE TO THE RESISTANCE SETTING OF SAID RESISTANCE DECADE; A DECADE SCALE ON SAID RESISTANCE DECADE CALIBRATED TO INDICATE NOMINAL CIRCUIT OUTPUT; A SOURCE OF FIXED REFERENCE VOLTAGE; A CALIBRATION METER HAVING A METER SCALE CALIBRATED TO READ PERCENTAGE DIFFERENCES PROPORTIONAL TO VOLTAGES APPLIED THERETO; AND VOLTAGE COMPARISON MEANS CAPABLE OF PRODUCING A VOLTAGE OUTPUT DEPENDING ON THE DIFFERENCE IN MAGNITUDE OF TWO VOLTAGES APPLIED TO ITS INPUT, SAID SOURCE OF REFERENCE VOLTAGE AND SAID SECOND CIRCUIT MEANS BEING CONNECTED TO THE INPUT OF THE VOLTAGE COMPARISON MEANS, SAID CALIBRATION METER BEING CONNECTED TO THE OUTPUT OF THE VOLTAGE COMPARISON MEANS, WHEREBY THE CALIBRATION METER SCALE INDICATES THE PERCENTAGE DIFFERENCE BETWEEN THE NOMINAL OUTPUT INDICATED BY THE DECADE SCALE AND THE ACTUAL OUTPUT APPLIED TO THE CIRCUIT OUTPUT TERMINALS, AND WHEREBY THE DECADE SCALE INDICATES THE MAGNITUDE OF OUTPUT ACTUALLY APPLIED TO THE CIRCUIT OUTPUT TERMINALS WHEN THE CALIBRATION METER HAS A ZERO READING.