Resolution, repeatability, reproducibility
Measurements & Uncertainties - OCR A-Level Physics
Key Definition
Resolution
The smallest change in the quantity being measured that an instrument can detect. Usually equal to the smallest reading the instrument can take. A 30 cm ruler with mm markings has a resolution of 1 mm. A digital stopwatch reading to 0.01 s has a resolution of 0.01 s.
The smallest change in the quantity being measured that an instrument can detect. Usually equal to the smallest reading the instrument can take. A 30 cm ruler with mm markings has a resolution of 1 mm. A digital stopwatch reading to 0.01 s has a resolution of 0.01 s.
Key Definition
Repeatable
A measurement is repeatable if the same experimenter, using the same equipment and method, gets the same results when the experiment is run again.
A measurement is repeatable if the same experimenter, using the same equipment and method, gets the same results when the experiment is run again.
Key Definition
Reproducible
A measurement is reproducible if a different experimenter, using different equipment or a different method, gets similar results.
A measurement is reproducible if a different experimenter, using different equipment or a different method, gets similar results.
- Resolution is a property of the instrument. Repeatability and reproducibility are properties of the experiment as a whole, including method and operator.
- An instrument with high resolution does not guarantee a low uncertaintyThe range of confidence in a measurement, written as ± a value giving the upper and lower bounds within which the true value is expected to lie.. A digital stopwatch reading to 0.01 s still has uncertainty of about 0.2 s when started and stopped by hand, because human reaction time dominates.
- A repeatable experiment may still be wrong. If you make the same systematic error every time, you get the same answer every time, but it is consistently off the true value.
- Reproducibility is the stronger test. If a different lab, with different kit, gets similar values, the result is trustworthy. OCR practical papers reward this kind of evaluation.
- See the figure below for a resolution comparison.
Diagram pending
Side-by-side close-up of a 30 cm ruler reading (smallest division 1 mm) and a Vernier caliper reading (smallest division 0.02 mm) measuring the same small object. Show how the Vernier scale gives one extra decimal of precision.
Will be replaced with a GeoGebra SVG in stream 2.
- Improving resolution: use Vernier calipers (0.02 mm) instead of a 30 cm ruler (1 mm), or a digital balance to more decimal places.
- Improving repeatability: tighten the method (fixed start position, same operator, same timing technique) and take more repeats.
- Improving reproducibility: write the method clearly enough for another student to follow without conversation. State all equipment specifications.
Common Mistake
HIGH
Wrong: Treating "repeatable" and "reproducible" as the same word. Or claiming an instrument with finer divisions is automatically "more accurate".
Right: Repeatable = same person, same kit. Reproducible = different person or different kit. Accuracy depends on how close the value is to the true value, not on how many decimal places the instrument shows.
Right: Repeatable = same person, same kit. Reproducible = different person or different kit. Accuracy depends on how close the value is to the true value, not on how many decimal places the instrument shows.
Examiner Tips and Tricks
- When OCR asks you to evaluate a method, comment on resolution of each instrument used, then say whether the result is repeatable, then comment on whether it would be reproducible by another student.
- The five-word checklist: resolution, accuracy, precision, repeatability, reproducibility. Use them precisely. Examiners notice when students swap them.