To measure resistance with an analog ohm meter,
first touch the probes of the meter together and adjust the zeroing
knob until the meter reads zero ohms. Once the meter is zeroed, place
the probes across the resistor to be measured. If the reading is too
high or too low to be meaningful, adjust the range of the meter. A
digital ohmmeter doesn’t require zeroing as an analog meter does.
The resistance function of a multimeter is also used to measure
continuity. This is useful for checking for breaks in wires or blown
fuses. A good wire or fuse should read zero ohms where a bad wire or
fuse will read infinite ohms. Many meters have a continuity function.
This sounds a buzzer when there is continuity.
An ohmmeter should never be connected to a circuit that has power applied.
very high resistances be sure you are not touching the probes. Your
body has a resistance of several hundred thousand ohms. When measuring
a low value of resistance, this doesn't make much difference. However,
when measuring something like 1,000,000 ohms (1 Megaohm), the reading
will be affected by your own resistance.
Analog meters usually have an “off” position. This shorts the inputs to
the movable coil together. As explained in DC motors below, this
dampens the movement of the needle when the meter is shaken, protecting
it from damage when the meter is bumped around when not in use. If you
have an analog meter, you can demonstrate this. Shake the meter lightly
and observer the needle movement. Now put the switch into the “off”
position and shake it again. The needle will move much less.