# A student measures the extension of a spring when a 500 g mass is hung from it. She takes five measurements using a ruler and records the following extensions: 42 mm, 43 mm, 42 mm, 58 mm, 43 mm. Describe how the student should process these results to obtain a reliable value for the extension, and explain why one of the readings should be treated differently from the others.

> AQA A-Level Physics (7408) — 3.1.2 Limitations of Physical Measurements · Describe · 5 marks

## Mark scheme (5 marks)

1. Identifies 58 mm as an anomalous result / outlier
2. States that the anomalous result should be excluded / not included in the mean calculation
3. States that the mean (average) of the remaining values should be calculated
4. Links calculating the mean to improving reliability / reducing the effect of random error
5. Explains that the anomalous result is likely caused by a random error (e.g. misreading the ruler / the mass swinging)

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