Hello! I'm trying to get the hang of bbt, I take it at the same time every day, I don't move around before hand etc etc but it still seems erratic. This morning I took my temp 3 times consecutively to see what it did. It came out 36.40, 36.14, and 36.47! So not very consistent! What bbt thermometers do you use as I'm thinking about getting a better one but don't want to spend a fortune! This is the one I have below. Thanks ladies X