Your Tools May Be Precise, But Are They Accurate?

July 2010

An issue that occasionally arises in our Calibration Lab is the difference between the precision and the accuracy of a tool. Precision is the least amount the tool indicates. Using a tape measure as an example, a tape measure with marks every 1/32nd of an inch is more precise than a tape measure that has marks every 1/8th of an inch. Accuracy is a measure of how the tool will measure against a reference standard. A multi-meter that indicates 1.000 Volts when a voltage of 1.000 Volts is applied would be more accurate than a multi-meter that indicates 1.010 Volts when the same 1.000 Volts is applied.

It is important to note that just because a tool is more precise does not mean it is more accurate and accurate tools do not always have the best precision. In our example of the tape measure, it could be precise to 1/32nd of an inch, but indicate 31/32nd of an inch when compared to a 1-inch calibrated standard. Our tape measure that is less precise with 1/8th inch increments could indicate 1-inch when compared to the same 1-inch calibrated standard.

If you have any questions or comments about this, contact Duncan Aviation Calibration Services at 402.479.1698.