Choosing the right ladder

What is a scale?

The scale of an axis indicates how many units each square on the grid represents. For example, if each square represents 2 seconds, ‘2 s’ is written at regular intervals along the axis.

How to choose a suitable scale

To choose a suitable scale, you need to:

1. Identify the largest value to be represented.
2. Divide this value by the number of squares available on the sheet.
3. Round to a whole number (1, 2, 5, 10, 20…) to make it easy to read.

Example

If the greatest distance to be represented is 48 m and there are 12 squares available, then 48/12 = 4. A scale of 5 m per square (a whole number and sufficient) should be chosen, rather than 4 m, which is less practical to mark out.

Common pitfall

An incorrectly chosen scale can either flatten the curve (the graph is too small and difficult to read) or, conversely, extend beyond the edge of the page (the scale is too small in relation to the values). The scale must also be regular: you must never skip an irregular step between two graduations (for example, 0, 1, 2, 5, 10 is incorrect).

Key points

A well-chosen scale makes maximum use of the available space whilst remaining easy to read and to mark out.