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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@halemmerich
Nope, not just you :)
There are several threads for this. Best summary currently is in this post: http://forum.espruino.com/comments/16454552/
Gordon has created a repository for collecting HR data to aid in the development of a better algorithm: http://forum.espruino.com/conversations/373033/#comment16554946
Short version is, movement is bad for accuracy and currently for sports a Bluetooth based ECG-HRM device helps a lot.