What’s The Difference Between Precision And Accuracy

Heidenhain High Accuracy Gages

When taking data measurements, precision and accuracy are two most important factors to consider. Both of them reflect how close we are to getting an actual value. However, there is a slight difference between the two. Precision gives the reproducibility of the measurements, even if they are nowhere near to the accepted value. Accuracy gives a number close to that of accepted or known value. It’s like hitting a bullseye. Measurements which are both accurate and precise are very near to actual values, and can be repeated.

How Are Both Of Them Defined?

According to physics, the consistency in results with repeated measurement readings is what we call precision. The values can be different from each other, and it’s known as observational error, in scientific terms.

On the other hand, accuracy has two common definitions. In engineering and science, accuracy measures the closeness to the actual value.  According to ISO, accurate measurements are true and consistent, without any random or systematic error.

Examples of Precision And Accuracy

You can think of precision and accuracy in terms of hitting a bullseye board. If the person is hitting the center target almost every time, he is highly accurate in doing that. However, if he doesn’t hit the target, but always strikes the same position on the board, he’s being precise. A person who is always hitting the center target in the same way has a high degree of both precision and accuracy.

Let us take a more practical example of accuracy and precision. If you take the mass measurement of a 100 gram sample and get values of 97.5, 97.6, 97.5 and 97.7 grams, the scale is quite precise, but not accurate. If you are getting values as 99.8, 100.5, 101.0 or 99.6, then it has higher accuracy than preciseness. Always remember the mnemonic that Accurate is correct or close to true value, while precision is something that repeats.

Precision, Accuracy And Calibration

What according to you is an ideal instrument? One that records precise measurement or an accurate one. If you are weighing yourself on a scale that gives you different readings every time, close to your real weight, then it is accurate. However, it might be more viable to use a precise scale. In this case, the measurements will be very close to the true value by the same amount, which is a common issue with scales. Most of them have a tare button to 0 them.

While balances and scales may give you an option of adjusting, in order to get both precision and accuracy, other instruments may require calibration. Thermometer is a good example, as they take readings in a certain range and give erroneous values outside that range. For calibrating an instrument, you need to record how far measurements are from the actual values. In order to ensure proper readings, maintain a record of the calibration. Equipment pieces may also require regular calibration to ensure precise readings, and you must seek professional help to get it done accurately.

by George Chitos