Multimeter accuracy

The following is the typical accuracy for a student-type digital multimeter, information often provided on the back of the meter. The shorthand notation (A + B) means that the uncertainty of the reading is guaranteed to be less than ±(A% of reading + B least significant digits):

1. Max counts 2,000 (e.g. 2.000 V or 200.0 mV or 2,000 ω)

2. <200 V dc (0.1 + 1) 45 Hz to 10 kHz (0.5 + 2)

3. <200 mA dc (0.3 + 1) 45 Hz to 10 kHz (1.0 + 2)

4. <200 kΩ (0.2 + 1)

5. >2 MΩ (0.5 + 1)

For example, for a reading of 1.453 V dc, the uncertainty is less than ±(1.453 × 0.1% + 0.0001) V. For a reading of 1.453 V ac, the uncertainty is less than ±(1.453 × 0.5% + 0.002) = ±0.009 V.

Note that in the latter case, the accuracy (adherence to the accepted standard) is ± 0.009 V, but the precision (ability to detect small changes) is one least significant digit, or ±0.001 V.

A triangular distribution with full width ±W has a standard deviation σ = 0.408W. So as a rule of thumb, the multimeter uncertainty can be thought of as representing approximately 2.5 standard deviations.