I found that it helped me.
Back when I was TTC Mason and I had no idea about anything it helped me to figure out I was Oing at about cd21 and was having a 35 day cycle, not having my period a week late every cycle like I thought.
We were wasting our BD efforts on cd14. I had no idea when I was Oing so when I started using it and was getting a pebble pattern when I was supposed to be Oing I was just so darn confused that I kept using it every day until the ferns appeared and they got stronger and thicker.

I discovered that a good thick layer of spit on the thing and leaving it to dry on a sunny windowsill, or helping it along with a hair dryer, gave me a good accurate result.