A.3.2—Plotting two variables

Put the explanatory variable on the horizontal axis and the response on the vertical axis unless the question requires otherwise. Use units, even spacing and a scale that fills the plotting area.

Plot measured points rather than joining them automatically; add a best-fit line only when a model or relationship is justified.

For enzyme concentration versus initial rate, each point represents a measured pair; a curved trend should not be forced into a straight line.

A line through the origin is a hypothesis, not a default, and extrapolation beyond the measured range needs justification.