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Accurate vs precise

Accurate vs Precise

Updated: 09/09/2020.

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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