Test probes create a physical connection between a conductor, wire or circuit, and the meter itself. Probes can be either passive or active. In the case of probes used with digital meters, these components can also carry additional microcomponents in the probe's tip to produce ancillary, in addition to primary, measurements.
The scale increments and displays various meter results based on ranges of induction, impedance or other electrical potential. Because today's meters typically offer a range of scales on the faces of these units, be sure that you are looking at the correct scale before attempting to read a result.
You need to calibrate periodically this equipment due to magnetic or other external impacts. The zero meter insures that the system will read accurately by allowing the user to reset the pointer manually until the scale displays 0, regardless of the desired scale.
One of the primary uses for voltage meters is to measure resistance on a wire or circuit. This process is typically measured in Ohms and typically ranges from 2 Ohms and up, depending on the need. The impedance adjustment sets the unit's scale, so that the user can identify the proper value within a range.
On the front of the voltmeter typically you will see a knob or button that reads scale. This appliance is used to establish the test value based on type. Depending on the particular unit, the scale can range from 0 volts up to a 110/220 volts in the case of house electrical test units.