DVM - Digital Volt MeterThis tool measures all the basic units of electrical power: AC voltage, DC Voltage, resistance, capacitance, ohms, and current. Nicer units will also measure frequency. Actually most geeks have a nice one and then a cheap crappy one for doing things that they know might immolate the device. Cheapo units are generally less accurate which can really matter when you're modifying a more complex circuit, like something you might connect to an Arduino. Even something as simple as a continuity test requires a multimeter. This can be used to test cables, fuses but also board soldered components. Does current pass between point A and point B? You can't tell just by looking at it.
DMM - Digital Multi-Meter
VOM - Volt Ohm Meter
DVOM - Digital Volt-Ohm Meter
FET VOM - Field Effect Transistor Volt Ohm Meter
FET VM - Field Effect Transistor Volt Meter
TVM - Transistorized Volt Meter
VTVM - Vacuum Tube Volt Meter
DVTVM - Digital Vacuum Tube Volt Meter
The first volt meter was a primitive galvanometer first invented by Hans Oersted in 1820. Oersted was just describing the effect of current on a compass needle. Later that year Johann Schweigger developed a moving coil galvanometer. Devices descended directly from this design were later used in the first telegraphs to detect the signals passing through the wire. It's been about 290 years since those first devices and now you can buy a cheap volt meter at a truck stop for under $10.
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