Understand the idea.
Understand the idea
A measurement answers two questions: how much, and in which unit? First identify the quantity. A fence requires a length measurement; a packet of seeds requires a mass measurement. The instrument must measure that quantity directly.
Then match its range and resolution to the job. A tape reaches across long distances, while callipers distinguish small differences in diameter. A display with many decimal places is useful only if the instrument is suitable and correctly calibrated.
Choose and apply a method
Before reading a scale, check its zero and look straight at the markings to reduce viewing error. With a ruler, use the zero mark rather than assuming the physical edge is zero. Keep the instrument aligned with the length being measured.
If an object starts away from zero, its length is the difference between its endpoint positions. Record the unit beside the result and justify the instrument using the required range and smallest useful division, rather than its appearance.
See the method in action.
Match instruments to quantities
Choose instruments and units for a 17 m fence and a 250 g seed packet.
Worked solution
- 1
Identify the fence measurement.
A fence needs an instrument whose range can cover a long distance.
- 2
Choose the fence instrument and unit.
A tape measure records the length conveniently in metres.
- 3
Choose the packet instrument and unit.
A suitable scale with gram resolution measures the seed packet's mass in grams.
Tape measure in metres; suitable scale in grams.
Use position readings
A strip spans ruler readings 1.8 cm and 9.6 cm. Find its length.
Worked solution
- 1
Identify the two endpoint readings.
Both readings are positions on the same ruler scale.
- 2
Subtract the starting position.
The separation of two positions is the end reading minus the start reading.
- 3
Check the direction and unit.
The strip is shorter than the end reading because it begins beyond zero; the unit remains centimetres.
7.8 cm
Try it yourself.
Check your understanding
Would a bathroom scale reliably measure 3 g of spice?
Show answer & reasoning
Usually no.
Usually no: a bathroom scale is designed for much larger masses and normally cannot resolve a change as small as . Use a kitchen or laboratory scale whose range and resolution suit the quantity.
Keep practising
6 worksheet questions · 12 marks
Read the questions online
- Choose a sensible unit for a swimming-pool length and explain it.2 marks
- Choose an instrument to measure 75 mL of liquid to the nearest millilitre.2 marks
- A window width must be checked to the nearest millimetre. Is a tape marked only every centimetre sufficient?2 marks
- A rod spans ruler readings 2.4 cm and 15.9 cm. Find its length.2 marks
- A carton is labelled 2 L. Is this mass or capacity? Name a suitable measuring instrument.2 marks
- Explain why reporting a width as 42.000 mm from a ruler with 1 mm divisions is misleading.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Choose a sensible unit for a swimming-pool length and explain it.2 marks
A pool is normally tens of metres long; millimetres would be unnecessarily small.
Metres. - Choose an instrument to measure 75 mL of liquid to the nearest millilitre.2 marks
It measures liquid volume and resolves the required 1 mL.
A suitable graduated measuring cylinder with 1 mL divisions. - A window width must be checked to the nearest millimetre. Is a tape marked only every centimetre sufficient?2 marks
A centimetre is 10 mm, so the marks do not directly resolve each millimetre.
No. - A rod spans ruler readings 2.4 cm and 15.9 cm. Find its length.2 marks
cm.
13.5 cm. - A carton is labelled 2 L. Is this mass or capacity? Name a suitable measuring instrument.2 marks
Litres measure capacity, not mass.
Capacity; a graduated liquid-volume measure. - Explain why reporting a width as 42.000 mm from a ruler with 1 mm divisions is misleading.2 marks
Choose a recorded precision consistent with the scale and reading method.
The decimal places imply more resolution than the ruler supplies.
Curriculum reference & lesson scope
SACE Board of South Australia
Stage 1 General Mathematics measurement skills and applications; original explanatory lessons and papers.
Official curriculum source ↗