Gradient

If substrate amount is plotted, the line falls as substrate is used. Its gradient is negative because the measured amount is decreasing, but a steeper downward line still represents faster substrate use; compare the magnitude of the gradients when comparing speed.

The average rate over an interval is found using two points and the gradient of the line between them. To estimate the rate at one particular time on a curved graph, draw a tangent at that point and calculate the tangent's gradient using a large triangle.