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Understanding Terms - Accuracy

Using multimeters to test circuit board

What is accuracy on a multimeter or clamp meter?

Accuracy refers to how accurate the displayed figure is compared to the actual value of the measured subject. 

The accuracy value given in the specifications of a digital multimeter will look something like,

“Basic accuracy ±0.5%  ± 2 dgt”

 

The term accuracy is often confused with count/digits, and resolution.  You can read our blog on Understanding Count, Resolution and Range for a full description of count/digits and resolution.

  

What do these figures mean?

“Basic accuracy ±0.5%  ± 2 dgt”

The first figure will give the percentage accuracy for a given range. In the above example 0.5%.  It means the displayed result could be 0.5% higher or 0.5% lower than what the real result should be. 

The second figure refers to the last, or least significant figure, on the multimeter display.  This last digit could be incorrect to plus or minus “that many digits”. In this case 2 digits. This error is in addition to the above mentioned percentage error.

Putting it together with an example - a multimeter with a 2000 count display is showing a result of 2.005V and has a basic accuracy of ±0.5% ±2 dgt. 

The percentage error is 2.005 x 0.5% =  0.01. Thus the real value of what’s being measured could be anywhere between 1.995V and 2.015V  (2.005 - 0.5% = 1.995V and 2.005 + 0.05% = 2.015V).

However, an included error of ±2 digits on the display means we have to push the last significant figure of these values out by another 2 digits.  Thus the real value of what’s being measured could be anywhere between 1.992V and 2.017V  (1.995V – 0.002 = 1.992V and 2.015 + 0.002 = 2.017V).

For a lot of users, such minor errors would be insignificant to the values they are looking for.  However, for some, small errors could increase fault finding difficulties dramatically.  Eg. when measuring outputs on sensors where the control circuitry is looking for very small changes.

As such, if accuracy is imperative to your measurements, be sure to check the specifications on the multimeter to ensure that the accuracy is suitable for your requirements.

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The example above uses voltage values. Delta Pro includes voltage basic accuracy in the  "Quick Stats" for most products. However, any function that a meter has will have a basic accuracy associated with a measurement. These basic accuracies can be found in the product specification sheets.