Tinkerbell, I know what you mean. If I insert the dilator and then see how far the lube goes, I can see that the outside of the curve has an inch less than the inside of the curve (where the dots are). But essentially, what I was told is that you use the dots to measure the depth. They range from 4 inches to 6 inches at 1/2 increments. And the measurement is taken where the dot is, not the other side. But if you were to get a tape measure and then measure the length to that dot, you have to use the outside of the curve. I know, its confusing. They had to repeat it to me twice to explain. So for instance, with my dilator, it goes in to the third dot. I use a mirror and see visually the dot disappearing inside. The third dot is supposed to be 5 inches. I previously thought it was 4 to 4 1/2 inches because I measured the length along the same curve as the dots. But they told me to measure on the outside of the curve. My dilators are transparent, so I can see where the dot is on the other side. And if I measure to that dot on the outside of the curve, it is indeed 5 inches!
Now all of this pertains only to my dilators and my own surgeon's advice. Your dilators might involve a different situation. You might want to see if the manufacturer has any advice on this.
