Using a voltmeter can be a relatively simple task if you know a few things about them. The two main types of voltmeters are analog and digital, and the latter is often referred to as a digital volt meter (DVM). Some voltmeters are dedicated units that only measure voltage, while others are just one part of devices that measure amperage, resistance, and other things. If a digital voltmeter can measure a number of things, it is often referred to as a digital multimeter (DMM). The most important thing to remember about using a voltmeter is to set it to the correct scale, and failing to do so may result in a blown fuse or damaged device.
Analog voltmeters may appear complex, though they are typically easy to read once you understand how they work. Many analog voltmeters have several arcs drawn on the meter face and a needle that can rotate from one side of the arc to the other. Numbers will usually be printed along the arcs, allowing you to read the voltage. The scale you select will determine which arc you use.
The scales on an analog voltmeter will usually be numbered according to the largest voltage they can measure. This means that the safest course of action is to choose a scale number that is larger than the voltage you expect. If you select too large a scale, the needle may not move or might move so little that you can not read it. In that case, you can always select a slightly lower scale without fear of damaging the meter.
Digital voltmeters often use scales as well, and other units may have an autoranging function. If it is possible to set a scale, choosing the correct one involves the same type of guesswork regarding the largest possible voltage, the same process as with an analog meter. Once it has been set up, the digital meter will allow you to read out a decimal voltage number, which can be easier than finding the right arc and counting the hash marks on an analog meter.
Voltage can be measured in parallel, so you can typically use a voltmeter without breaking the circuit you are testing. Measuring a voltage is typically as simple as touching the negative probe to the negative side of a circuit and the positive probe to the positive side. This is different from using an ammeter, since amperage must be measured in series.