I agree with ltweety you need one with 2 numbers after the decimal point. It wouldn't be accurate enough otherwise. And also try to get one that remembers that temp when you turn it back on again - it helps as I often go back to snoozing a bit before picking up my phone to enter it in FF. One word of warning, try not to over analyse your temps after O. It's so hard but I found it took me on an emotional roller coaster (as if TTC isn't enough of one anyway!) I cried over dips, got excited over rises and it became a bit too much. I'm thinking of ditching it next cycle - if you look at my past two charts you'll see what I mean (although I wasn't TTC on the first chart) It's fab for helping with predicting O though. Good luck. Xx