Record exactly what you observed, when you observed it, with the units and the instrument used. Then explain it. A strange reading that is honestly recorded and thoughtfully discussed is worth more than a perfect-looking table that did not come from your experiment.
This matters in practical science, ICT tasks, fieldwork and any project where your own evidence is assessed. Your school and Cambridge set the exact rules for assessed work.
Why is it tempting to change the numbers?
Readings rarely look like the textbook. You expect a pattern, your results do not show it, and you worry the work will look like a failure. Adjusting one number seems harmless.
But the point of practical work is to show that you can collect evidence and interpret it. Invented numbers remove the thing being assessed. Real scatter, with a good explanation, is the skill.
How do I record observations properly?
- Write readings as you take them, in a table prepared in advance, not from memory later.
- Include units in the column headings and keep the same decimal places as the instrument allows.
- Keep every repeat, including the odd one. Mark it, do not delete it.
- Add a short note next to anything unusual: what happened, what you changed.
- Calculate afterwards, in a separate step, and show the working.
Worked example
A student times a trolley rolling down a ramp three times with a stopwatch: 1.42 s, 1.38 s and 1.51 s.
The raw table keeps all three. The mean is (1.42 + 1.38 + 1.51) ÷ 3 = 4.31 ÷ 3 = 1.4367, which is 1.44 s to two decimal places.
The range is 1.51 − 1.38 = 0.13 s. A fair note reads: “The third time was slower than the mean of the first two (1.40 s) by 0.11 s. Possible cause: I started the stopwatch late. A light gate would reduce this error.”
The mistake to watch for
A student finds the third reading “too different” and writes all three as 1.40 s, because that looks consistent.
Now the record says there was no variation, which is not what happened. The table also no longer supports any conclusion about reliability. The correction is to restore the real readings and explain the difference.
Self-check
- Two readings are 12.1 N and 12.5 N, and a third, 14.0 N, looks odd. What should you do?
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Record all three. Mark 14.0 N as unusual, suggest a reason (for example, the spring was not at rest), and consider repeating the measurement. Do not delete it silently.- Calculate the mean of 12.1, 12.5 and 12.3.
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12.1 + 12.5 + 12.3 = 36.9, and 36.9 ÷ 3 = 12.3.- You forgot to record one temperature reading. What is the right first step?
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Tell your teacher and follow their instruction, which may be to repeat the practical. Never write a guessed value as if it were measured.When might one-to-one tuition be worth considering?
Self-study works if you already understand tables, units and averages. Tuition may be worth considering when you can collect the data but cannot explain a surprising result, or when your evaluations are thin.
A teacher can practise on original data with you, so your own assessed work stays your own. Read the guide on feedback versus completed work, the rules check for AI and our Physics tuition page.