Learning Library · Multimeters, explained · 1
Counts, digits, and resolution
"3½ digits", "6,000 counts", "4⅚ digits": multimeter datasheets describe the same thing three different ways. All of them answer one question: how many steps the display can show before it has to change range. Pick a meter, feed it a voltage, and watch where the decimal point goes.
The display shows the reading on the selected range. The bar shows how much of the display's count is in use; the row below shows the meter's voltage ranges, with the active one highlighted.
Type a value, drag the slider, or pick a preset.
Counts: the number that matters
A digital multimeter converts the input into a whole number of steps, called counts, and then places a decimal point and a unit on it. A 6,000-count meter can show any number from 0 to 5,999. On its 6 V range that is 0.000 V to 5.999 V, so one count is 1 mV.
The same 6,000 counts on the 600 V range are 0.1 V each. Resolution is not a fixed property of the meter. It depends on which range the reading lands on, and an autoranging meter picks the lowest range that fits.
Where the ½ comes from
Digit ratings count the display positions. Every position that can show 0 to 9 is a full digit. The leftmost position on many meters cannot, and the fraction describes how far it goes.
| Display count | Largest reading | Written as | Leftmost digit |
|---|---|---|---|
| 2,000 | 1999 | 3½ | 0 or 1 |
| 4,000 | 3999 | 3¾ | 0 to 3 |
| 6,000 | 5999 | 3⅚ | 0 to 5 |
| 20,000 | 19999 | 4½ | 0 or 1 |
| 60,000 | 59999 | 4⅚ | 0 to 5 |
| 200,000 | 199999 | 5½ | 0 or 1 |
| 2,000,000 | 1999999 | 6½ | 0 or 1 |
There is no strict standard for the fraction. Some datasheets write 3⅚ as 3¾ or 3.8, and 4⅚ as 4.8, and a "4,000-count" and a "6,000-count" meter can both be called 3¾ digits. When two meters are hard to compare, compare the counts.
Try this
- On the 6,000-count meter, enter 5.999 V. Autoranging puts it on the 6 V range, using 5,999 of 6,000 counts, with 1 mV resolution.
- Now enter 6.001 V. It no longer fits, so the meter steps up to the 60 V range and shows 6.00 V. Resolution falls to 10 mV and the last digit is gone.
- Switch to the 20,000-count meter with 6.001 V. It lands on the 20 V range and keeps the 1 mV digit: 6.001 V.
- Enter 120 V for mains. The 6,000-count meter reads 120.0 V on its 600 V range. The 2,000,000-count meter reads 120.0000 V, with 100 µV resolution.
- Choose the 6 V range by hand and enter 6.001 V. A manual range does not step up, so the display shows OL, for overload.
Reading UNI-T labels
UNI-T's UT8000E bench multimeters run from 4½ to 6½ digits. Their published display counts are the clearest way to compare them:
| Model | Display count | Digits |
|---|---|---|
| UT8802E | 19,999 | 4½ |
| UT8804E | 59,999 | 4⅚ (listed as 4.8) |
| UT8805E | 199,999 | 5½ |
| UT8806E | 1,999,999 | 6½ |
On a UT8802E, for example, the 2 V range resolves 100 µV and the 20 V range 1 mV, exactly Range ÷ 20,000. Handheld meters are usually rated by count alone: the UT171B and UT181A are 60,000-count meters, and the UT196 and UT197PV are 6,000-count meters.
Resolution is not accuracy. A 2,000,000-count display tells you the smallest step the meter can show, not how close that step is to the true value. The accuracy specification answers that question, and it is the next explainer in this series.
More counts, more digits you can keep. UT8000E bench multimeters from 4½ to 6½ digits.
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