This simulates a dartboard. The aim is to illustrate the idea behind using the Standard Error of the Mean (SEM) to
estimate how well we could know the mean given the number of datapoints.

Press N to add a datapoint. Press it for a while to get maaaaanyyy datapoints. Press A to show the averages, S to show the standard deviations and D to show the SEM.
Press P to show/hide the position of the average point, and E to show ellipses corresponding to the SD:s (green) and SEM:s (blue).
Press space to show all but the actual values. Press V to show the values used in the calulations. Press C to restart.