Difference between Accuracy and Precision

ACCURACY

Accuracy has many definitions but all definitions give the same meaning in many ways.

Accuracy is the ability to provide exact or true value,

In case of measurement, it is the ability of the measuring instrument to obtain true or exact value in a measurement.

Accuracy is the proximity or closeness of the measured value with true value.

PRECISION

It is the ability to reproduce the same value or

It is the ability of the measuring instrument to reproduce the same value again and again.

Example:

Let us consider a weight measuring instrument which measures the weight of steel cube. Exact weight of the steel cube is 50 kg.

CASE 1:

In first trial, the instrument shows weight of the cube as 49.899 kg.

In second trial, the instrument shows weight of the cube as 49.973 kg.

In third trial, the instrument shows weight of the cube as 49.935 kg.

In fourth trial, the instrument shows weight of the cube as 49.907 kg.

From the above observations, we can conclude that the instrument has some accuracy since it gives the output value which is near to the exact value 50 kg. But the instrument is not precise since it gives different value for each measurement.

CASE 2:

In first trial, the instrument shows weight of the cube as 47.819 kg.

In second trial, the instrument shows weight of the cube as 47.823 kg.

In third trial, the instrument shows weight of the cube as 47.835 kg.

In fourth trial, the instrument shows weight of the cube as 47.847 kg.

From the above observations, we can conclude that the instrument has some precision since it almost reproduces same output value 47.8 kg. But the instrument does not have accuracy since the measured values are not closer to the actual weight 50 kg.



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