Fertile days log

I don't know if this is something being worked on, or if it's already been asked. This is my 2nd cycle after BC so glow is just starting to get a grip on my days (no AF on BC so nothing previous to log) I'm going to be using OPKs to pinpoint my fertile day. If it's different from the apps idea, is there anyway of adjusting it? Or should I just pop it in my notes for now?