Instead of plotting points on a graph we sometimes plot lines representing the uncertainty in the measurements. These lines are called error bars and if we plot both vertical and horizontal bars we have what might be called "error rectangles", as shown below

x was measured to ±0·5s
y was measured to ±0·3m

The best-fit line could be any line which passes through all of the rectangles. Assuming that the line passes through zero, use the example above to estimate the maximum and minimum slopes of lines which are consistent with these data. (The diagram is too small to expect accurate answers but you should find about 1·06ms^-1 maximum and about 0·92ms^-1 minimum.)

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