The gradient measures how steeply the line rises, and in physics it usually carries real meaning, such as a spring constant or a speed. To find it, first draw the best-fit line, then choose two points that lie exactly on that line, not two of your original data points.
Pick the two points far apart, near opposite ends of the line, and form a large right-angled triangle between them. A large triangle reduces the effect of small reading errors, so the gradient comes out more accurate.
Read the coordinates of both points carefully, then calculate the gradient as the change in y divided by the change in x. Show these values clearly in your working.
Because the gradient is read from the line rather than a single measurement, it smooths out scatter and often gives a more reliable result than any one data point could.
What examiners award
Marks are awarded for using two points on the best-fit line, a large triangle, correct coordinate reading, and the correct change-in-y over change-in-x calculation.
Common mark losses
In short
The gradient is the change in y divided by the change in x, read from two well-separated points on the best-fit line. Use a large triangle for accuracy.
A routine that works
Practise the mechanics until they are automatic: label both axes with units, choose a scale that fills more than half the grid, plot points with a sharp pencil, draw a single best-fit line, and take the gradient from a large triangle with its coordinates and unit shown. One clean example beats re-reading the theory.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)