Open switch top left area is D.C. motor (3600 r.p.m.) 10 K ohm adjustable resistor (rheostat in generator current control language) is to set range of right 0 - 1 M amp meter. Center switch should be DPDT either toggle or slide switch used to reverse polarity to meter depending on motor direction.
Hold eraser against motor shaft to steady meter reading.
Calibrate meter using known rpm motor or better result, a variable speed motor with a laboratory stroboscope.
