The super-cool Google Jules Verne demo that went up today reminded me that I made an accelerometer tester for the iphone ages ago.
It's an offline app, so don't be afraid to "add it to home screen" - and if you don't want to get dizzy, then lock the phone to portrait mode!
It just uses a dodgy implementation of some "sparklines" to plot the X, Y, and Z rotation that you can fetch by listening to the
devicemotion event. It should work in Chrome - but doesn't seem to. I'll check it out, and update this post with some more details tonight. Or tomorrow night. Or.