Accurate vs Precise

Accurate vs Precise

In every day speech, terms “accurate” and “precise” are used interchangeably, as synonyms. In mechanics, especially in measurement, the meaning of these two terms differs. Since I am and will be using these terms, it would be wise to clearly define them.

Before giving any (boring) definitions, I think a picture will speak a lot more clearly:

1: Accurate and precise 2: Inaccurate and precise 3: Accurate and imprecise 4: Inaccurate and imprecise
1: Accurate and precise
2: Inaccurate and precise
3: Accurate and imprecise
4: Inaccurate and imprecise

Definitions, before an explanation in “plain English”:

  • Accuracy: how close is the value gained by measuring to the real value.
  • Precision: how close are the results of each repeated measurement (of the same object) close to each other.

Let us take weight (mass) measurement for an example. Say we are measuring a 70 kg heavy cyclist, using 4 different scales and repeating the measurement 3 times in a row with each scale. Measurement results are shown in table below:

Scale1st
measurement
2nd
measurement
3rd
measurement
1707070
2686868
3697170
4646665
  • Scale 1 is both accurate and precise.
  • Scale 2 is very precise, but not accurate.
  • Scale 3 is pretty accurate, but not very precise.
  • Scale 4 is neither accurate, nor precise.

As can be seen in this explanation, terms accurate and precise are connected and somewhat similar, but not exactly the same.

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