Error bars show the uncertainty in plotted values. Each bar is a line through the point, extending the same distance above and below it (or left and right) equal to the absolute uncertainty in that value. Short caps are drawn at the ends.
• Use the absolute uncertainty of each value, which may differ from point to point.
• Draw vertical bars for uncertainty in y and horizontal bars for uncertainty in x.
• If the uncertainty in x is too small to show on the scale, the horizontal error bar is left out.
• If you plot a calculated quantity, such as T2, find its uncertainty first using the combining rules.Using error bars: the true value of each point is expected to lie within its bar, so the line of best fit should pass through every error bar. A point whose error bar is not reached by the line of best fit may be anomalous and should be checked. If many bars are missed, the uncertainties may have been underestimated or the relationship may not be linear.Error bars are also used to draw worst-fit lines, which give the uncertainty in a gradient and intercept (next lessons).
• Use the absolute uncertainty of each value, which may differ from point to point.
• Draw vertical bars for uncertainty in y and horizontal bars for uncertainty in x.
• If the uncertainty in x is too small to show on the scale, the horizontal error bar is left out.
• If you plot a calculated quantity, such as T2, find its uncertainty first using the combining rules.Using error bars: the true value of each point is expected to lie within its bar, so the line of best fit should pass through every error bar. A point whose error bar is not reached by the line of best fit may be anomalous and should be checked. If many bars are missed, the uncertainties may have been underestimated or the relationship may not be linear.Error bars are also used to draw worst-fit lines, which give the uncertainty in a gradient and intercept (next lessons).