This ARM Tool is designed to read the resistance of all 1/24 & 1/32nd scale type Armatures one stack at a time. Turn on meter and place the armature to be tested in place, between the two measuring posts. Turn the slot in the commutator facing up. Rotate the metal stack and gently press down to make contact until the meter reading is steady. Record the reading & subtract the tolerance posted on the rear of the meter. All 3 readings can be done in less than 10 seconds.