Measure BPEL (Bone Pressed Erect Length) the same way every time, that is how to track your gains. Do several measurements, record the number that you get several times.
I wait until I am about 10 minutes into the erection to make sure it is fully erect.
Some say BPFSL (Bone Press Flaccid Stretch Length) is a better tracking measurement, but for me it HURTS LIKE HELL to do that. And it takes about 3 days to recover from. So I don’t do that.
Girth can be tricky. Measure the same place everytime. Again take several measurements, record the number you get several times.
Some measure base, midshaft, and right under the head. That could be a good idea - I mostly measure midshaft, but from pictures I can see that I have gained between midshaft and head.
I think it is a good idea to take pictures. YOu don’t have to post them here, but they are nice to have to compare.
I am not sure that chasing “my finger and thumb doesn’t touch” is that important.
I think that is a direction that porn-starlets receive from directors. “Make sure you fingers don’t touch while you are blowing him.”
There is at least one guy with 6+ inch girth who has said he has never met a woman that could not wrap her hand around him with thumb and finger touching.
Erect penises compress, so they can compress to your grip when you wrap your hand around it.