I think it's best when you don't look at it until after a long time. I say this because my mom did a big chop to this date last year. She came to visit me and it was very emotional because she had suffered so much hair trauma and did not want to cut it off.
I suggested that she chop due to the condition of her hair and the fact that she didn't want to relax anymore, and we went to a salon for a second opinion. Upon the stylists's recommendation, she went for the BC!! I see my mom only a few times a year (about 4) and each time it looks so much longer. I'm with her this weekend after not having seen her for about 5 months, and her hair is soooooooooo long!!! She's been sporting wigs the whole time and keeping her hair underneath in plaits. I promise, it must be about 7 or 8 inches long all around, and it's all natural. When she chopped it it was relaxed. It's so thick and long.
Even she didn't realize how much it had grown because she just covers it up all day. And she didn't take vitamins! All she did was use MNT poo and con, and WGO on her scalp.
Comparison pics are a great way to chart your growth too if you are wigging it or wearing a protective style. I took pics last year of my mom after the BC, and I'm going to take some this weekend. Hopefully she'll let me post results on my site for inspiration
Sorry for going on so long about my mom, but the short answer is that I think when it's left alone and you look at comparison shots, that's how you really know it's growing and how much.
HTH,
SG