# In Digital Multimeter note accuracy in digits

I have digital Multimeter noted in the multimeter accurcy is range 0 - 1000v at 0.2% +30 digits in this range what is 30 digits?

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I don't understand what's being asked. Exactly what is written on your multimeter? "0 - 1000v at 0.2% +30 digits"? –  trygvis Nov 2 '12 at 7:35
Question is clear to those with the knowledge to answer. –  Chris Stratton Nov 3 '12 at 13:21
@Chris: The question is so poorly worded that it is not clear. Perhaps English is not the OP's first language, but I expect this would be a runon sentence in any language. –  Olin Lathrop Nov 3 '12 at 16:37
@OlinLathrop the question is very clear to those who care to understand it. Those who do not care or do not wish to be of assistance need not concern themselves. –  Chris Stratton Nov 3 '12 at 16:40

+/- 30 digits indicates the 'absolute error' of the value displayed means that what ever value you read on the display, you have to add / subtract max. 30 from the display value to find the range the actual value is in.

For example your multimeter shows 10.00V then:

• add 30 ticks to find the upper limit 10.30V
• subtract 30 ticks to find the lower limit 09.70V

So your actual value will be between 9.70V and 10.30V

This also illustrates why you have to choose a measuring range that fits the measured value best. If you choose a too high range, the absolute error will render your measurement completely useless. Look at this example:

• subtract 30 => -0.20V

Which is an entirely useless result, the actual value ranging from -200mV to +400mV due to bad range and its absolute error. In such a case choose a better (lower) range.

You didn't ask about it, but your relative error was 0.2%. Back to the 9.70V - 10.30V example:

• The lower limit will be 9.70V - 0.2% = 9.68V
• The higher limit will be 10.30V + 0.2% = 10.32V

So when you read 10.00V on your multimeter, the actual value will range somewhere between 9.68V and 10.32V.

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Usually, the word used is "counts", not "digits". It's a reference to the counter used in the typical dual-slope ADC commonly used in digital multimeters.

There are basically two limits to the accuracy of such a meter: The precision of the components used in the analog side of things gives you a percentage-of-reading (or percentage-of-range) error, and the accuracy of the timing circuits on the digital side gives you the ±counts error.

The possible error on any particular measurement is generally going to be the larger of these two numbers.

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