BRAINCAKEPrecision and Accuracy
Precision describes how close repeated measurements are to each other. Precise readings have a small spread. Poor precision is caused by random errors.
Accuracy describes how close a measurement is to the true value. Poor accuracy is caused by systematic errors, which shift readings away from the true value in one direction.
The two are independent. Think of darts on a board: darts grouped tightly but away from the bullseye are precise but not accurate; darts spread widely around the bullseye are accurate on average but not precise; a tight group on the bullseye is both.
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Key terms in this lesson
- random error
- An error that causes repeated readings to vary unpredictably above and below the true value.
- systematic error
- An error that shifts every reading from the true value by the same amount or proportion, in the same direction.
More in Measurements and Uncertainties
- Random and Systematic Errors
- Absolute and Percentage Uncertainty
- Combining Uncertainties
- Uncertainties from Repeated Readings
- Plotting Graphs
- Error Bars
- Best-fit and Worst-fit Lines
- Uncertainty in a Gradient and Intercept
All 12 lessons in Measurements and Uncertainties · All OCR AS-level Physics topics