Small decimal values, and data bunched far from zero where a non-zero start is the right choice.
Practice data: Decimals (0.14, 2.4) and data such as 78–148 or 84.1–85.6.
Decimals use the same easy steps
0.1, 0.2 and 0.5 are easy steps too, as are 0.01, 0.02 and 0.05. Data up to 0.55 A on 10 big squares: 0.55 ÷ 10 = 0.055 → round UP to 0.1 per big square.
When to start an axis above zero
If the data is bunched far from zero (heart rates of 78 to 148 beats/min, or a mass of 84.1 to 85.6 g), starting at 0 squashes it into a thin strip and it will not use more than half the grid. Then it is right to start the axis just below the smallest value, at a round number.
Show the start clearly: write the first value at the origin. Many teachers like a small zig-zag "break" on the axis to show it does not start at 0. Do NOT start at a non-zero value when the data begins near 0, and never for the bars of a bar chart.
Find the range: smallest to largest (78 to 148 = 70).
Divide by the big squares (70 ÷ 10 = 7) and round UP to an easy step (10).
Start at a round number just below the smallest value (50 or 70), and check the largest value still fits.
The SLAPUK mark scheme
SLAPUK
Out of 5 (S L A P U). Out of 6 (S L A P U K) when there is more than one data set on the graph.
S
Scale
Even steps of 1, 2, 5 or 10 (×10ⁿ), and the data uses more than half the grid each way. Never use the raw data as your scale.
L
Line
Join the points with straight lines using a ruler, point to point. Best fit only when the question asks.
A
Axes
What you changed goes on x, what you measured goes on y. Copy the table headings as the labels.
P
Plots
Every point within half a small square, drawn as a small × or ⊙.
U
Units
Units after a slash or in brackets: "Time / min" or "Temperature (°C)".
K
Key
Only for two or more data sets: a key that says which line is which.
Practice graphs
1. Current through a resistor
The current through a resistor was measured at different voltages.
Plot a graph of current against voltage. Join the points with straight lines using a ruler.[5 marks]
Results Illustrative data
Voltage / V
Current / A
0
0
1.5
0.14
3
0.27
4.5
0.41
6
0.55
1 · Axes, labels and scales
Put Voltage / V (the independent variable) on the x-axis and Current / A on the y-axis. This grid is 8 big squares across and 10 up; each big square has 5 × 5 small squares.
Set your scales, then tap the grid to plot each point.
Keyboard and screen-reader entry
Values are placed using the scale you set, so a wrong scale still gives a wrong graph – just like on paper.
Stuck on the scale?
y: 0.55 ÷ 10 = 0.055 → round UP to 0.1 A per big square.
