I distinctly remember experiencing this before starting any PE whatsoever. At first, I was worried that it was due to otherwise unnoticable injuries caused by my beginner’s routine (kegels and jelqing), but I for example recall that my first measurements had to be quite quick, since my penis really wasn’t that interested in the tape. But since this seems to be generally normal, and I experience no other problems whatsoever, I’ll try to not let it bother me.