Accurate Measurement
Use a range of scientific equipment to take measurements with increasing accuracy and precision. Take repeat readings when appropriate.
What a learner can do afterwards
- Use scientific equipment (scales, thermometers, measuring cylinders, stopwatches) with increasing precision
- Explain why repeat readings improve reliability and take at least three readings
- Identify and deal with anomalous results (measurements that don't fit the pattern)
1 · Read
You have practised measuring carefully. Match the tool to the quantity: a thermometer measures temperature, a stopwatch measures time, scales measure mass, and a ruler measures length. Ask an adult for help with hot liquids.
Take at least three readings under the same conditions for this lesson's repeat checks. Compare how much they vary. Repeats can reveal a slip, but agreement does not prove that the tool or method is correct. In a ramp test, keep the release point and finish line the same. If the release point changes, label that result separately instead of treating it as a repeat.
An anomalous reading does not fit the others' pattern. Possible causes include a mistake, changed conditions or real variation. Keep the original record. Check the equipment and method, then repeat carefully. Never change a value to make it match. Explain any later decision about whether to use it.
A measuring cylinder measures liquid volume in millilitres. Choose one that holds the water and has clear scale marks. Place it upright on a level surface. For water, read the bottom of the curved surface at eye level. No instrument gives a perfectly exact measurement.
Mass readings of 42 g, 42 g and 48 g include two matching readings. Count the matching pair: two readings agree. That agreement alone does not establish their accuracy.
Length readings of 9 cm, 9 cm and 16 cm make 16 cm anomalous: it is far from the matching pair. Investigate it; do not delete it automatically. For decimal times, the digit after the point counts tenths of a second. Compare whole seconds first, then tenths if needed. Times of 7.2 s and 7.5 s both have 7 whole seconds. Their difference is three tenths, or 0.3 s. A reading of 14.8 s is far from that pair.
Accuracy is closeness to a true or accepted reference value. Precision is how closely repeated readings agree. Readings can be precise but inaccurate: they can agree yet all differ from the reference. For repeated lengths that differ from a known reference, check the ruler's zero mark and endpoint alignment. More readings with the same faulty setup can repeat the same offset.
Exclude a reading only for a justified reason, such as measuring another object or timing beyond the finish by mistake. That time includes more than the journey. Keep the value and explain its exclusion; repeat after a timing slip. For a total, add accepted readings one at a time. Add ones, then tens. Exchange ten ones for one ten and ten tens for one hundred. For 47 + 58, 15 ones and 9 tens become 105. A total is not an average.
Scale divisions affect the detail you can read. One centimetre contains ten millimetres. A ruler marked every millimetre shows smaller length differences than one marked only every centimetre. Align the object's end with zero and read straight down.
The range describes the spread of readings. Find the largest reading and subtract the smallest. Subtracting finds the difference. You can count up from the smallest to the largest. For readings of 6 cm, 8 cm and 7 cm, count from 6 to 8: two centimetres. The range is 8 − 6 = 2 cm. Whether a range is acceptable depends on the task.
To find a mean, add the readings and divide by their number. Division makes equal shares, one per reading. Share tens equally, then deal out ones one at a time. For 42 ÷ 3, split 42 into 30 and 12. Each share gets one ten and four ones, making 14. Times of 4 s, 5 s and 6 s total 15 s; their mean is 15 ÷ 3 = 5 s. A mean summarizes readings; it does not remove a shared offset.
Choose suitable equipment, compare repeats, and investigate unusual readings. Keep the original record and explain any exclusion.
The three rewritten readings were written for this dataset. One reading and seven additional questions written for this dataset. Video lessons by TED-Ed.
2 · Watch
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Where it sits
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Where this leads
15 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.