It took me a while to get the hang of charting. At first I didn't realise how important consistent timing was, etc. I also started off originally with a mercury thermometer...

After 2 years of it, I now have a much better idea of when to accept or reject FF's interpretation. For example, this cycle it tried to tell me I O'd on CD12, which I knew was complete rot because I know my post-O temps are over 36.5. Once I actually had 3 temps over 36.5 it shifted my O day to CD16 (which I agree with).

Hopefully you'll get your BFP before you have time to become an expert on charting!