Most scales only label some of their marks. Before reading one, work out what each small mark is worth. Find two labels next to each other, take the smaller from the larger, and count the spaces between them (not the lines). Divide to find the value of one space. Then start at the last label before the pointer and count on the marks, adding that value each time. On a jug labelled every 100 mL with 4 spaces between labels, each mark is 25 mL.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- scale
- a line of marks and numbers used to measure
- interval
- the space between two marks next to each other
- label
- a number written next to a mark
Worked examples
A tape is labelled 0, 10, 20 with 5 spaces between labels. The arrow is 3 marks past 10. What length is it, in cm?
- 1.10 ÷ 5 = 2, so each mark is 2 cm.
- 2.3 × 2 = 6, and 10 + 6 = 16.
= 16
A jug is labelled every 100 mL with 4 spaces between labels. The water is 3 marks above 200. How much water is there, in mL?
- 1.100 ÷ 4 = 25, so each mark is 25 mL.
- 2.3 × 25 = 75, and 200 + 75 = 275.
= 275
A kitchen scale is labelled every 500 g with 5 spaces between labels. The needle is 2 marks past 1000. What mass does it show, in grams?
- 1.500 ÷ 5 = 100, so each mark is 100 g.
- 2.2 × 100 = 200, and 1000 + 200 = 1200.
= 1200
For parents
Method: Work out what one mark is worth
What to say: What do the labels go up by? How many spaces are between them? So what is one mark worth?
Common mistakes:
- Assumes every small mark is worth 1, whatever the labels go up by.
- Works out the value of one mark by dividing by the number of marks between labels instead of the number of spaces.
- Counts the labelled mark as the first step, so reads one mark too far.
- Reads the nearest labelled number and ignores the unlabelled marks after it.