OK, you can't resist some metrics, and you might want to write up your project for the journals.
So keep a daily journal. The real metrics are the things that happen in the real world. Write in your journal every day at a fixed time, recording the events of the previous 24 hours. Evening is probably best for memory, if it works for you.
Here are some things Ron has been asked, or asked himself, that he sometimes wishes he had written down:
Number of classes and methods by date
Number of test classes, methods, and asserts by date
Number of stories available by date
Number of stories replaced, destroyed, split by date
Daily journal of feelings and observations
Significant events or comments made by people