Yeah I think it’s natural, but definitely magnified when doing PE because of the various stages of trauma/fatigue/recovery we go through.
For me, I’m finding the ‘range’ more helpful in relation to the subject of PI. Typically I’ve read about PIs, and specifically negative PIs, as far as reduced EQ and difficulty getting and maintaining erections. For a while it didn’t exactly click with me because even after intense hanging I still felt I had good EQ etc. I’ve found that personally ( and maybe for others ) my negative PIs are much more subtle.
My penis always remains functional, but tracking my BPFSL daily has given me insight into when I need to take a day off.
For example, the day before yesterday I measured 6.8125 BPFSL. Yesterday it was barely 6.75 or a bit under. Mentally I wanted to do PE, but I took the day off. Today, I measured just about 6.875. This is a pattern I’m seeing consistently.
So yeah, to summarize: I think fluctuations are good for judging when you need rest.
To judge gains progress, I think that’s where the importance of consistent measuring comes in. Despite fluctuations, the data will clearly show consistent progress over time.