Fraction Sense

Watched a nice video about Dor Abrahamson talking about how math is, or should be, about making sense.



In this video he describes a device to let students play with a proportion, and I thought it would be simple enough to do in GeoGebra, so... here you go! I'm pretty happy with the sketch, it's clean and the controls should be simple enough for young students.  Close means within 5%, and Wow! is within 1%, so it's easier with a large unit. There's a lot of research supporting introducing fractions with a comparison model before the typical part-whole model, so it's nice to have a tool for that.

Available as a GeoGebra file or dynamic webpage. I've mostly stopped embedding GeoGebra files on the blog because it adds to load time significantly, it seems faster as a separate webpage.What other fraction representations would you like to see in a dynamic representation?

EDIT:
Made this before GeoGebraTube! I've updated this a little with a practice mode and more sensible checking. Here's the Teacher page (download) or the Student page (applet). Also have made this multiple choice fraction estimation applet.