Read a graph in four looks before you write a word: what the axes are, what the units are, what shape the line makes, and what specific numbers you can quote. Only then draw the conclusion.
The four looks
- Axes. Which quantity is on each axis? This matches the variables you already identified.
- Units and scale. Does one square equal 1 or 10? Does the axis start at zero?
- Shape. Rising, falling, levelling off, straight or curved.
- Numbers. Pick two or three points and quote them with units.
Doing the looks in this order stops the most common error, which is describing a shape without knowing what it is a shape of.
A worked example
A graph shows the temperature of hot tea in a cup, taken every 2 minutes. At 0 minutes it is 90 °C. At 4 minutes it is 70 °C. At 8 minutes it is 56 °C, and at 16 minutes it is 40 °C.
- Axes: temperature (°C) upward, time (minutes) along.
- Shape: the line falls, steeply at first and then flattening.
- Numbers: it fell 20 °C in the first 4 minutes but only 14 °C in the next 4 minutes, and 16 °C in the 8 minutes after that.
A full conclusion: the tea cools fastest when it is hottest, and the rate of cooling slows as the temperature gets closer to the room’s.
The misreading to avoid
Suppose a student writes: “The graph goes down, so the tea loses the same amount every minute.” That is a shape-only conclusion, and the numbers disprove it, since 20 °C in the first 4 minutes is 5 °C per minute, while the fall from 8 to 16 minutes is 16 °C over 8 minutes, only 2 °C per minute.
Quoting two readings would have caught it. That is why the fourth look matters.
Scales can mislead
Two graphs of the same data can look different if one axis starts at 50 instead of 0. A line that seems to drop sharply may fall only a few degrees. Always read the numbers on the axis before describing how steep anything is.
Try it yourself
A plant-height graph shows 4 cm at week 0, 10 cm at week 2 and 16 cm at week 4, forming a straight line. Describe the relationship and give the growth per week.
Answer
Height increases steadily as time increases, forming a straight line. Growth is (16 − 4) ÷ 4 = 3 cm per week, and the check at week 2 gives 4 + 2 × 3 = 10 cm, which matches. The line does not pass through the origin, since the plant was already 4 cm at week 0, so height is not directly proportional to time.
Where to go next
Once you can read a graph, checking whether evidence supports a claim is the natural next skill. For the straight-line case, revisit calculating a straight-line gradient, and you can test motion graphs on the motion-graph explorer. If graph questions still cost marks, one-to-one Science tuition lets a teacher hear your first reading and correct it.