Until recently I always used a steel ruler below the pubic bone with a single layer of cloth as a buffer just above the shaft. Lately I’ve been doing some home improvements and happened to have a short piece of smooth T&G floorboard that was about 8” long and thought Hmmm.
I can press the tongue side of this across the top of my unit (below the pubic bone) and press as hard as I like with no discomfort whatsoever since the pressure is distributed (always an issue with the ruler). I’ve lost measurement length doing this, but find it far more consistant, so I think I’ll stick to it for regular measurements. Psychologically I think it’s better too, instead of getting caught up on the numbers and wondering why I’m 1/8” smaller than yesterday, and if it was my breakfast, or time of day that I PE’d that maked the change.