As an employee or entrepreneur it could be great to keep track of your own productivity to improve your work-ethic.
This could be considered a Core metric of yourself. Be careful it is not a vanity metric but something meaningful.
Make sure that you keep records as historical data is important for metrics.
Reference
Ferriss, Timothy. The 4-Hour Workweek: Escape 9-5, Live Anywhere, and Join the New Rich. Expanded and Updated ed., 1st revised ed, Crown Publishers, 2009.
Highlights or timestamps
he keeps track of how much work he does with quantifiable records
— ^c6634a from The 4-Hour Workweek