another weigh to go !

Two scales, one green and one blue are placed some distance D apart. A rigid board is placed across the two scales, and both scales are adjusted to read zero. Enter the value of the mass to be placed on the board. Slide the mass along the board. Can you explain the readings? Is your explanation a model of the data? Is it a model of why the scales work as they do? What questions could/would you ask your students based on this applet?
Can you devise a way to weigh a 350 lb. motorcycle using a bathroom scale whose upper limit is 200 lb ?