The handheld digital multimeter (DMM) is the most common of all electrical and electronic test instruments. Following are some important performance specifications that need to be considered. Display Digits - The display must be capable of showing the reading depending upon the application. For a process where the whole 7-digit display is required, a three-and-a-half-digit display would prove useless.
Resolution - Resolution is a measure of the smallest increment that may be discerned. Higher the resolution, better the DMM. Although this is not true in all cases, as other parameters like applications, measuring rate, etc. are also considered.
Accuracy - It is the probability of the reading being accurate. High accuracy is always preferred. Uncertainty - It is a characteristic considered with conjunction to accuracy; i.e. if there is a 1% uncertainty with a DMM, it will give out readings that are 99% accurate. Manufacturers use this term to indicate how the device may go wrong in practice.
Repeatability - It is often more important than absolute accuracy when making a series of measurements. It is the degree of measurement that will give out the same reading each time a measurement is repeated.
Calibration - It indicates how well the DMM has been tested against various quantity measurements and how closer they were to the intended value.
True RMS - RMS measurements are a measure of the equivalent heating effect produced by a voltage and, to be accurate, must include any DC component present along with the AC component that most users associate with RMS readings.
Crest Factor - It is defined as the ratio of the peak or "crest" voltage compared to the RMS voltage.
Form Factor - It is defined as the ratio of the RMS value to the average value and is the factor that when multiplied by the average value of a waveform will equal the RMS value.
Environmental & Safety ratings - The DMM has to be checked for being insensitive to environmental changes, and that they were manufactured by abiding to various safety norms that are enlisted by different international electrical safety commissions.