Here’s something I notice about the ruler also. You really have to straighten your back out as you measure and compensate for the slight angle you are looking from. Try to measure with your head and neck as straight as possible. Usually, with an erection, most men have a tendency to stick it out a bit and lean their back out slightly. Considering the penis is sticking out further than your head and neck, you are looking from a slight angle which can give the illusion it might be slightly off in measurement. The longer your unit, the worse the angle as you have to bend your neck to try to get your eyes lined up directly over the measurement.
That angle can easily throw you off considering that your head is already at an angle compared to where your shaft is, usually coming up slightly lower unless you have an upward curve. The angle issues are also much worse with a transparent ruler. Also, if your erection has a slight curve to it, a lot of men tend to straighten it out against the ruler causing them to press against it. That extra pressure, if you aren’t careful, can enlarge the penis slightly forcing and trapping more blood into it, also throwing off the measurement.
You probably already accounted for this, but I’m just sharing a little bit of the problems I’ve faced when measuring with the ruler.
