Precise is not the same as accurate
Show on a big screenA thermometer shows 82.3, 82.4 and 82.3 °C. Each number is a reading: one number you get from a tool. The water is exactly 80 °C.
The rule
Accuracy is closeness to the true value. Precision is how fine and steady the readings are.
Accurate readings are close to the true value. Precise readings are fine in detail and steady. Repeats agree.
Some books say precision is fine detail. Others say it is readings that agree. Both uses are common. Detail from a finer tool counts.
The thermometer is precise but not accurate. Its readings agree with each other. All of them are about 2.3 °C too high. For example, 82.3 − 80 = 2.3 °C.
| Readings (°C) | Steady? | Close to 80 °C? |
|---|---|---|
| 82.3, 82.4, 82.3 | Yes | No |
| 80.1, 79.9, 80.0 | Yes | Yes |
| 70.5, 92.0, 88.5 | No | No |
The bullseye is the middle of the target. Darts far apart but centred on it are accurate on average.
Extra digits printed by a program add no detail. Only a finer tool does. A ruler marked in whole centimetres gives 7 cm. A program may print 7.0000 cm. The extra zeros add no new fact.
Metadata is facts that describe the data, such as the tool used.
Move the sliders. Make the mix.
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