iOS Heart-rate monitor

A project I'm working on currently.

For those who care, it's a iOS heart-rate monitor for use with Bluetooth Smart devices.
The coloured ring shows individually calculated training zones ranging from 50% (yellow) to 100% (red) of the users maximum heart-rate.
Current zone is displayed on the top left and also visualised by the the black indicator.

Don't forget to check the attachment for the full shot.

Any kind of feedback is welcome!