Mean, Median, and Spread
Change the values of any of the 9 blue data points by moving them horizontally with the mouse or by changing the numerical coordinates in spreadsheet column A to the right. Select checkboxes and observe how the Mean, Median, and BoxPlot of the data set vary as an individual point is moved.
Select MAD or Variance to move a slider giving an estimate of the "center" M as the spread is shown. When trace is also selected it is possible to recognize which values of M minimize MAD or Variance. You can also select animate to slowly vary M.