An Introduction to the Resolution of Digital Multimeters
Resolution indicates how fine an instrument's measurement results can be. By understanding a meter's resolution, you can determine whether tiny variations in the measured signal can be observed. For example, if a digital multimeter has a resolution of 1 mV on the 4 V range, you can observe minute changes of 1 mV (1/1000 of a volt) when measuring a 1 V signal.
If you intend to measure lengths shorter than 1/4 inch (or 1 mm), you certainly would not use a ruler marked only in inches (or centimeters). For a temperature reading of 98.6 °F, a thermometer with only integer‑degree markings will be useless. You need a thermometer with a resolution of 0.1 °F.
Digits and counts are terms used to describe meter resolution. Digital multimeters are classified according to the digits and counts they can display.
A 3½‑digit meter features three full digit positions ranging from 0 to 9 plus one half‑digit (which can only display 1 or remain blank). A 3½‑digit multimeter delivers a resolution of 1999 counts, while a 4½‑digit multimeter achieves 19999 counts.
Describing resolution in counts is preferable to using digits. Some 3½‑digit multimeters have improved resolutions of 3200 or 4000 counts.
Multimeters with 3200 counts offer better resolution for certain measurements. For instance, a 1999‑count meter cannot resolve down to 0.1 V for voltages above 200 V. By contrast, a 3200‑count meter can still show 0.1 V increments when measuring up to 320 V. When measuring voltages higher than 320 V while requiring 0.1 V resolution, a higher‑priced 20000‑count multimeter is required.
