In Digital Multimeter note accuracy in digits

+/- 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:

Your display reads 00.10V:

• add 30 => 0.40V
• 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.