In reply to Patrick803:
I've had loads of problems with mine. I sent it back to Suunto. The service is pretty good and they replaced it. It's been OK since but not perfect - still some slight dimming of the display.
I think it is to do with the software on the older Core, but if you have a new one it shouldn't be that. If you google it you should find some details and check with your serial number.
I also have a Suunto HRM which has been perfect.