d) Uncertainty graphs

d) graphical treatment of errors and uncertainties; line of best fit; worst line; absolute and percentage uncertainties; percentage difference

The absolute uncertainty of a measurement is shown by an error bar on a graph

The bar is drawn along the x- or y-axis and starts from the minimum uncertainty to the maximum uncertainty

A line of best fit and a line of worst fit is used to calculate the gradient of an uncertainty

The line of best fit passes as close to the points
The line of worst fit is the steepest or shallowest line that passes as close to the error bars

Percentage uncertainty of the gradient = (best gradient - worst gradient) / best gradient × 100

Percentage uncertainty in the y-intercept = (best y-intercept - worst y-intercept) / best y-intercept × 100

Percentage difference is