Appendix B

Graphing

Course Support
Lab Contents
 

Slope Calculations with an exact fit

Figure 7

An example of the special case where all the data points line dead on a line and the uncertainties are too small to show as error bars. Determine two widely spaced locations on the best fit by selecting an x value and reading the y value with a reading uncertainty from the graph scale. Do not use data points or data values that where used to plot the graph.
  
slope   =   \[\frac{(174 \pm 1) - (118 \pm 1) c}{(110-40)s}\]
  =   \[\frac{56 \pm 2}{70}\]
  =   \[\frac{56c \pm 3.6\%}{70s}\]
  =   \[0.800c/s \pm 3.6\%\]
  =   \[0.800 \pm 0.029 c/s\]
 

It is important to emphasize that the slope with its uncertainty is calculated from the graph and not from data used to plot the graph.