Click some points, then click Update to calculate the minimum diameter spanning tree. Length is shown in the Java Console.
Click Detail to toggle the disks with the selected centers.
Click Animate (sorry) to toggle between L2 and Linfty; you must click Update for the display to be recalculated, and you probably want to click Detail so that you can see the disks and know whether you have L2 or Linfinity.
Random picks 30 random points.