OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
Analysis: (c) appropriate use of significant figures
Significant figures communicate how precisely a measurement was made.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 2 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Significant figures communicate how precisely a measurement was made. In practical biology, the number of significant figures you report should match the resolution of the instrument and the precision of the data, not simply the digits shown on a calculator. For example, a balance reading 2.34 g has three significant figures, so a mean of several such readings should be quoted to three significant figures, such as 2.36 g, not 2.3617 g. Leading zeros are never significant, trailing zeros after a decimal point are significant, and zeros between non-zero digits are significant. When multiplying or dividing, the answer takes the smallest number of significant figures in the inputs; when adding or subtracting, it follows decimal places. Round only at the final stage to avoid accumulating error.
What earns the marks
- Identifies that the number of significant figures reported should reflect the precision and resolution of the measuring instrument.
- States that leading zeros are not significant while trailing zeros after a decimal point are significant.
- Applies the rule that a product or quotient is quoted to the smallest number of significant figures present in the input values.
- Recognises that rounding should be carried out only at the final stage to avoid accumulating rounding error.
- Distinguishes significant figures from decimal places when adding or subtracting values.
Common mistakes and how to put them right
Counting leading zeros as significant figures.
Put it right: Zeros before the first non-zero digit are placeholders and are not significant.
Quoting every digit shown on a calculator display.
Put it right: Round the final answer to the significant figures justified by the input data.
Rounding intermediate values during a multi-step calculation.
Put it right: Carry full precision and round only the final result.
Exam tips
- Read the question carefully to see whether it asks for significant figures or decimal places, as the two rules differ.
- Check each input value's significant figures before deciding the precision of your final answer.
- Show your unrounded value and then your rounded answer so the rounding decision is visible.
Try the lesson
The start of the Analysis: (c) appropriate use of significant figures lesson, made from checked teaching notes for this specification point.
Have a go first
A student records a length as 12.50 cm. How many significant figures does this value have?
Listen
Significant figures communicate how precisely a measurement was made. In practical biology, the number of significant figures you report should match the resolution of the instrument and the precision of the data, not simply the digits shown on a calculator. For example, a balance reading 2.34 g has three significant figures, so a mean of several such readings should be quoted to three significant figures, such as 2.36 g, not 2.3617 g. Leading zeros are never significant, trailing zeros after a decimal point are significant, and zeros between non-zero digits are significant. When multiplying or dividing, the answer takes the smallest number of significant figures in the inputs; when adding or subtracting, it follows decimal places. Round only at the final stage to avoid accumulating error. A strong answer earns marks for these points. Identifies that the number of significant figures reported should reflect the precision and resolution of the measuring instrument. States that leading zeros are not significant while trailing zeros after a decimal point are significant. Applies the rule that a product or quotient is quoted to the smallest number of significant figures present in the input values. Recognises that rounding should be carried out only at the final stage to avoid accumulating rounding error. A common slip: Counting leading zeros as significant figures. Instead, zeros before the first non-zero digit are placeholders and are not significant. Exam tip: Read the question carefully to see whether it asks for significant figures or decimal places, as the two rules differ.
See it
Key words
Say what each word means before you turn the card.
Precision and resolution of measurements
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Rules for identifying significant figures
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Rounding conventions in calculations
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Reporting data honestly and consistently
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See every definition
- Precision and resolution of measurements
- The number of significant figures reported should match the resolution of the instrument and the precision of the data, not simply the digits shown on a calculator.
- Rules for identifying significant figures
- Leading zeros are never significant, trailing zeros after a decimal point are significant, and zeros between non-zero digits are significant.
- Rounding conventions in calculations
- When multiplying or dividing, the answer takes the smallest number of significant figures in the inputs; when adding or subtracting, it follows decimal places.
- Reporting data honestly and consistently
- Round only at the final stage to avoid accumulating error.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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