It's extremely self-explanatory, as students are asked to measure different angles and come up with solutions for various problems that are a little less "regurgitory" in nature (ex: What do you notice about the two angles?)
As always, this site works great on a SMART Board. I would suggest, however that there's an even better way to use this site (Windows users only...sorry fellow Mac diehards).
1. Drag the protractor that's provided by the site off to the side.
2. Open SMART Notebook software and find the usable protractor (found under the Math measurement tools button).
3.. Finally, put Notebook into "transparent background" mode, by clicking on the tool that looks like a computer monitor with a white screen (only available in the Windows version at the moment).
The great part about this is that the kids can now have access to the full intuitive features of SMART's protractor, and can write and erase with ease over top of the website (no more digital ink layer necessary).
Either way, it's a nice way of building small group collaboration into a centers-based classroom where the activity doesn't always lead to a simple right or wrong answer, but lends itself to discussions and critical thinking.
Have a great weekend.