I don't use the cbfm but I use those new clear blue ovulation tests that basically test the same way, they monitor estrogen and LH. So u either get low, high (flashing smiley) or peak (solid smiley) and today I got my first ever solid smiley on cd26!!! I have long irregular cycles so never known when I ovulate. As it's so late in my cycle I have used two packs of sticks so it was getting expensive and frustrating but I'm glad I stuck with it! Finally a 2ww that I know I'm actually in!
Good luck xx