Any idea how to teach significant figure in a meaningful activity that EJS can make?

This is the most popular java applet on significant figure.

But the teaching approach is more drill and practice, I was thinking about a more powerful way to allow students to explore.

reference:

http://lectureonline.cl.msu.edu/~mmp/applist/sigfig/sig.htm

My initial idea.

1. box for learner to key in values ( types real numbers, scientific notation )

2. EJS logic(s) evaluate the input and display the correct number of significant figures.

doesn't seems to be a good and useful applet to make, do you have an idea(s) to add as well? ;D