A Multimeter combines in one unit several measurement functions such as voltage, current and resistance. Digital multimeters (DMMs) are generally more accurate and easier to read than their analog counterparts. While analog multimeters indicate the value with a needle over a scale, a digital multimeter has an LED or LCD display. A digital multimeter can be a hand-held device for field work or a bench instrument which can measure to a very high degree of accuracy.
DMMs offer a variety of measurements. Most include the basic measurements of current (DC and AC), voltage (DC and AC), and resistance. Additional measurements offered by most DMMs include capacitance, temperature, frequency, transistor test, and continuity. It is important to consider the maximum and minimum reading capabilities.
One important factor to consider is whether the DMM will measure true RMS values. True RMS measures the actual heating effect of the waveform. A DMM that does not measure true RMS values measures the average of the absolute value of AC voltage and are calibrated to the RMS value for a sine wave. This average reading calibrated for RMS values is sufficient form many applications.
A DMM's resolution defines how small a change in measurement can be seen. Digits and counts are used to describe resolution. DMMs are classified by the number of digits displayed. A 3-1/2 digit meter displays 3 full digits from 0 to 9, and one "half" digit which displays only a 1 or is left blank.
Accuracy refers to the uncertainty of a reading due to inaccuracies in the DMM. Typically a handheld DMM will provide accuracy levels of around 0.5%, while bench multimeters can provide accuracy of 0.01%.
An important requirement for a DMM is its compatibility with a wide variety of accessories that can increase the measurement range and usefulness. These include a wide range of probes such as high-voltage and current probes, temperature probes, and RF probes. For connecting to the circuit, there are a number of test leads, test probes, and test clips.