Figure 6.

Gaussian fit to mastery data. The number of student users plotted against the Weber fraction of the difficulty level at which mastery was demonstrated. The data for each practice session have been fitted with Gaussian distributions in order to see more easily the shift toward lower Weber fractions with each session. The R² values (goodness of fit) for sessions 1 through 6 were 0.87, 0.67, 0.77, 0.81, 0.93, and 0.92, respectively.