I track my biorhythms. Have since I read one of the first books about them. First by hand with stencils cut to the cycles on graph paper and then on computer spreadsheets.
Interestingly, there are a few people who write that biorhythms (Br) are pseudo-science, meaning almost-science or mimic-science. That's what the genius editors at Wikipedia let through the last time I checked. That's for them to figure out. The charts match my experience and that's good enough for this n = 1.
That's the prolog. To the classic 3 cycles—23 day physical cycles, 28 day emotional cycle, and 33 day mental cycles—I made a 4th. It's a average of the other 3, cept it never drops under zero. This ranges from nearly zero—I joke that people should check my pulse—to about 8—throw me in a lake to cool off.
As I puzzled over how much to set as my work time everyday it occurred to me that I could map the average cycle. Say it's 6.4 today, that would be 6.4 hours or 6 hrs, 24 min. This is very cool as I'll give myself more work time when my numbers are higher and I feel less fatigue, and less work time when they are lower and I tire faster.
Trying it this week and will report back.
R