Learn the 3-Step Method
1Read a point.
Find the time on the x-axis, go up to the line, across to the value: at 1pm it was 16°.
2Read the slope.
Rising line = getting warmer; falling = cooling. Steeper = changing faster.
3Read between points.
Halfway between 9am (8°) and 11am (12°), about 10° at 10am — the line estimates it.
Worked Example
From the graph: when was it warmest, and how much did it cool from 1pm to 5pm?
Watch Out! Common Mistakes
Order! Start from the TIME on the x-axis, go up to the line, then across — not the other way round.
Wrong chart! Favourite colours aren’t continuous — joining them with a line invents meaningless in-between values. Use a bar chart.
Careful! It cooled by 6 degrees, to 10°. ‘By’ is the change; ‘to’ is the final value.
⬇ Cheat Sheet
- x-axis: time. y-axis: the measurement.
- Point value: up from the time, across to the axis.
- Slope up = increase; down = decrease; steeper = faster.
- Only continuous data belongs on a line graph.
Quick summary
- Line graphs show change over time: up from the time, across to the value.
- Rising line = increasing; falling = decreasing; steeper = faster change.
- You can estimate between plotted points on continuous data.
- 'Cooled by 6°' is the change; 'cooled to 10°' is the final value.
Frequently asked questions
What is a line graph for?
Showing how something continuous changes over time — temperature, height, distance. The connecting line lets you estimate values between measurements.
How do you read a value from a line graph?
Find the time on the horizontal axis, go straight up to the line, then straight across to the vertical axis for the value.
Why can't favourite colours make a line graph?
Because there's nothing between the categories — a line would invent values between 'red' and 'blue' that don't exist. Categories belong on bar charts.
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