Line graphs

When the thing you change is a number that can take any value, such as temperature, time or length, a line graph is best. Put what you changed along the bottom (the x-axis) and what you measured up the side (the y-axis). Plot each result as a cross and join them with a line or a smooth curve.

When the thing you change is a set of separate groups, such as types of material, use a bar chart instead. A line graph lets you read values between your measurements: go up from the x-axis to the line, then across to the y-axis.