FSL is flaccid stretched length. Many prefer it to track gains rather than BPenis EnlargementL as you dont have to take into account varying erection hardness, just stretch and measure. Most non-Penis Enlargement'ers seem to have the same BPFSL and BPenis EnlargementL. I did starting out, then usually you have a higher BPFSL than BPenis EnlargementL after Penis Enlargementing for a while.
My BPenis EnlargementL is 7.5 or 7.625 on a good day but BPFSL is always 8.
Some say FSL is a sign of what gains are coming your way.