# Determining the uncertainty in the y-intercept using maximum and minimum gradientsDetermining the uncertainty in the y-intercept using maximum and minimum gradients

We can also determine the uncertainty in the y-intercept by using lines of maximum and/or minimum
gradients through their scattered data points. What happens when there is little scatter of the data
points? This is again when we can draw error bars.
a. Error bars may be added to each plotted point if the data points are not too scattered.
b. Draw a best fit line through the scattered points (or through the error bars). The worst
acceptable line is then drawn. This will either be the steepest or shallowest line.
c. Determine the y-intercept of the worst acceptable line and the y-intercept of the best fit line.
d. Uncertainty = |y-intercept of best fit line – y-intercept of worst acceptable line|.
e. The percentage uncertainty in the y-intercept can be determined as follows:
> Percentage Uncertainty = (Uncertainty/y-intercept) x 100