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Systematic error
Intermediate
A consistent bias from instruments or method, repeated every measurement.
A systematic error shifts all measurements in the same direction by the same kind of cause: a mis-calibrated instrument, a zero error, or a flawed method. It cannot be reduced by repeating the same experiment; you must find and correct the cause, for example by calibrating against a known standard.
A stopwatch that runs 1% fast makes every measured time 1% too long, however many trials you take.
Good precision can hide a systematic error, because the results agree with each other and look trustworthy.
In more detail
A systematic error shifts all measurements in the same direction, such as a zero offset or a miscalibrated instrument. Repeating the measurement does not reveal it, so it must be found by checking against a known standard.
Real-world uses
- A stretched measuring tape consistently underestimates lengths, a systematic error that affects a whole survey.
- Thermometers can have a fixed calibration offset that makes every reading too high.
- A balance that always reads 0.02 g too high gives every sample a bias, and no amount of repetition will reveal it without a reference mass.
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Frequently asked questions
How do I detect a systematic error?
Compare your instrument with a trusted standard, or use a different method to measure the same quantity.
Can averaging remove a systematic error?
No. Averaging reduces random scatter, but a systematic offset stays in the average.
How do I check for zero offset on a balance?
Measure a known reference mass, or read the display with nothing on the pan. Any non-zero reading is a systematic offset to correct.
Related topics in Measurement & Math Tools
Significant figures · Rounding rules · Accuracy vs precision · Random error · Absolute error · Relative and percent error