I may be biting into the cult it seems and have decided to start proper measurement myself too. SO, do you measure wet or dry hair? From the forehead down or from the top of your head?
I had measured 78cms before deciding to grow it, then had a trim Xmas time and now it is even less before I started out. 73,5cm OUCH!
I want to do it properly, or at least follow the common method. So which is that??
Thank you ladies!

edited to correct stupid mistake gone un-noticed for so long!

i measure after i washed (no waves!) and when it's dry cuze wet hair is longer and i just don't think one could measure properly since the length difference will increase with humidity (one would have to measure the humidity first to be able to interprete the hair length).
and from the front hairline so you will be able to hold easily the tape and measure from the same spot every time!

Being consistent is the most important thing.  Curly hair is easier to measure when wet.  I think most straight/wavy haired people measure when dry.

I personally don't measure every month, as it is too hard and too depressing to see the small increases.  Quarterly measurements seem to work best for me if I feel the need to measure.

Thank you ladies!
So, dry it is. And from the forehead down.
Thanks again.