S1.1.2—Measurement variables

Choose and prepare the instrument

Match range and resolution to the expected value and required precision. Check calibration, zero, units and viewing geometry before measuring mass, time, length, volume, temperature, force, current, potential difference, angle, sound intensity or light intensity.

Variable	Suitable instrument or method	Precision check
Mass; time	Balance; timer or data logger	Resolution is small enough for the expected change
Length; volume	Ruler/caliper/micrometer; measuring cylinder/burette	Avoid parallax and use the correct meniscus/zero
Temperature; force	Thermometer/probe; force meter	Use a suitable range and allow the reading to stabilize
Current; potential difference	Ammeter; voltmeter	Connect correctly and select a safe range
Angle; sound/light intensity	Protractor; calibrated sensor	Align the reference and control position/orientation

Read the value

Record enough digits to reflect the instrument’s resolution and include the unit. For a corrected reading, apply the zero offset with the correct sign; a displayed value is not automatically the true value.

Worked example — signed zero correction

A caliper shows $20.60\,\mathrm{mm}$ around a sphere but reads $-0.30\,\mathrm{mm}$ when closed. True diameter $=20.60-(-0.30)=20.90\,\mathrm{mm}$ . Subtract the zero reading algebraically; do not guess the correction direction.

Improve reliability

Repeat measurements, average them, and measure at different positions or orientations when geometry permits. This reveals random variation and reduces its effect on the mean.

Common trap

Do not increase precision by writing extra decimal places that the instrument cannot resolve, and do not correct a zero error in the wrong direction.

How it is assessed

Questions calculate a corrected caliper diameter or suggest an improvement using the same instrument.

Command terms

Calculate / State

What earns marks

Subtract the signed zero error correctly, or propose repeated measurements/averaging or measurements across different diameters.

Watch for

Adding rather than subtracting a negative zero error or proposing a new object instead of improving measurements with the same caliper.

Evaluate responsibly

Name the physical hazard or ethical trade-off and connect it to consequences and benefits.

Measure honestly

Check zero, units and resolution; repeat suitable measurements, average them and report only justified precision.

S1.1.2—Measurement variables

Measure with Suitable Precision

S1.1.2 Exam Analysis

Assessment in practice

Retrieve Experimental Practice