A digital multimeter, also called a DVOM (Digital Volt/Ohm Meter), is a tool used to measure various properties of electrical circuits and components, typically voltage, resistance, amperage, and continuity. Some multimeters are also equipped with ways to test diodes and transistors, but it is quite rare to encounter an automotive repair that requires testing those components.
A multimeter differs from an ohmmeter or voltmeter in that it can do what both of those tools do in one unit. A multimeter can also test amperage, but an ammeter can typically test higher amperage by measuring the magnetic field signature it leaves around a wire.
Analog multimeters also exist, but have been the less common option for a long time.
- Category I
- Category II
- Category III
- Category IV
Multimeter categories were designed with residential/commercial power distribution service in mind, so there are some requirements for each category that aren't listed because they generally don't apply to automotive applications.
Category one multimeters are the first rating and have the lowest level of protection within them from the four total categories.
Note that these categories are not a guarentee that the multimeter you own or buy will perform as described. One factor to consider is the condition of the meter; casing damage and damaged leads will reduce the safety of using the multimeter, regardless of the category rating.