1. A CALCULATING DEVICE FOR DETERMINING THE VALUES OF PARALLEL PAIRS OF RESISTOR EQUIVALENTS COMPRISING: (A) A BASE MEMBER BEARING INDICIA OF KNOWN RESISTOR VALUES, SAID INDICIA BEING LOGARITHMICALLY SPACED CIRCUMFERENTIALLY ON SAID BASE, THE CIRCLE THUS FORMED COMPRISING ONE ORDER OF MAGNITUDE OF THE LOGARITHMIC SCALE; AND (B) A DISK ROTATABLY MOUNTED ON SAID BASE MEMBER HAVING A FIRST SET OF RADIALLY DISPOSED OPPOSED REGISTRATION MARKERS, SAID MARKERS CONSTITUTING AN UPPER ARM AND A LOWER ARM, A RADIALLY DISPOSED REFERENCE MARKER POSITIONED 45 DEGREES TO THE LEFT OF SAID UPPER ARM WHEREBY WHEN SAID REFERENCE MARKER IS IN REGISTRY WITH ONE OF SAID CIRCUMFERENTIALLY SPACED REGISTER VALUES SAID FIRST SET OF MARKERS REGISTER WITH VALUES OF RESISTORS WHEN PARALLELY ARRANGED ARE EQUAL TO THE VALUE OF REGISTRY WITH SAID REFERENCE MARKER.