Precision vs Accuracy | Difference between Precision and Accuracy

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Precision vs Accuracy

Precision refers to the closeness of two or more measurements to each other, Whereas Accuracy refers to the closeness of a measured value to a standard or known value.

This is often confused. It can be very clear with an example.

Consider we are taking a measurement for the diameter of the shaft which is manufactured.

The diameter of the shaft should be 10mm.

Precise ( But not Accurate)

If you keep measuring the same shaft for frequently it will give the similar values respectively 10.9mm, 11.2mm, 11.05mm, 11.15mm. the average value for these measurements will give a maximum difference, that means error as shown below. Less the error More accurate is the instrument.

This is called precision. but not accurate, because the average value is not nearer to the known or required value 10mm.

Accurate (But not Precise)

So now it will make sense that accuracy is nothing but the closeness of the actual(Average measurement) value to the required value. Take another shaft, measure the diameter, the measurements are as follows 10.5mm, 10.3mm, 10.1mm, 9.8mm, 9.6mm. The average value is close to the known or required value. this is accurate

As explained above, the error (Difference between the average values, and  Required/known value) is less when compared to above scenario. this is accurate. But not precise

Why not precise?

“Because the measurement readings are much scattered from the average value. so it is not precise.”

Precise and Accurate

See the following scenario where both accurate and precise

Here, the measurements not scattered from the average value as well as the required value. So this can be both precise and accurate.

This is the difference between the precise and accurate/ Precision vs Accuracy

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