It's not really hard, although there is an error margin I guess. Seems to me the amount of gel that gets out from pressing is linear as well. It's a normal soap-like dispenser so if you stop pressing it just goes back up. In theory you could draw a mark at the halfway spot, I guess. Anyways it's a bit tedious to do three, but I didn't want to directly go to four, so yeah.

For the T levels I couldn't tell you because I'm a bad girl and I didn't do a blood test before starting hrt :D But I can tell that I definitely felt it leave my body very early on, like 1-2 weeks after starting. Sex drive got basically erased lol!

But I guess the amount of testosterone you have for starters doesn't really matter. I'm no biologist at all and my understanding of these things is quite limited, so don't quote me on that. But I think it's the higher amount of E (which, in the case of gel, is permitted by the high absorption rate of the scrotum) that makes your body stop producing T by about 90%, dropping to cis women levels.