Plotting and interpreting graphs
A well-scaled graph makes the trend, scatter and anomalies visible without distorting the evidence.
Use axes covering at least half the grid, accurate points, error bars where required and a single best-fit line or curve.
By the end of this lesson, you can:
- choose axes and simple scales;
- use most of the plotting area;
- plot points accurately;
- draw an appropriate best-fit line or curve.
Axes and scales
Put the independent variable on the horizontal axis and the dependent or transformed variable on the vertical axis. Label both as quantity / unit and choose scales that are easy to read.
Plotting
Plot small, precise crosses. Use more than half the available grid in both directions. Check any point that appears inconsistent before treating it as anomalous.
Best fit
Draw a single thin line with a balanced distribution of points above and below. Do not join point-to-point. A smooth curve is appropriate only when the expected relationship is curved.
Try another worked problem
Attempt the question yourself, then reveal the examiner-style solution when you are ready.
Best-fit line
Should a best-fit line join every plotted point?
CHECK YOUR ANSWERReveal solution
No. It represents the overall trend with balanced scatter, not a point-to-point path.
Mastery check
A best-fit straight line should normally have: