Ali- do you mean charting your temps? If so this is just a rough guide as to when you have O and helps you better understand your cycle. After O your temps rise (due to progesterone) and stay raised for 2 weeks. When AF is due you usually see a sharp drop in temps (progesterone levels fall) and the witch arrives soon after.

IVF meds can mess with your temps though. So not really that useful for us but I'm still doing it to watch when AF is due (although it didn't stop me from POAS last cycle Lol).