Sorry to sound daft here- I'm a conception newbie so please humour me. I just don't understand why people use these? I know they detect the LH surge etc, but if the egg lives for 24 hours and the sperm lives for up to 7 days, surely if you are having sex once a day you don't need to know the specific ovulation moment?
(As an aside- I have followed the fertility awareness contraception method for years so I am pretty aware of my ovulation signs and CD).