same idea as a HPT,,,,,, urinate on a stick (or dip in
urine), wait a few minutes, and if you get 2 lines equal in
color, you should ovulate within the next 48 hours....So you should BD that day and for a couple of days after......There are more in depth instructions that come with them......I find it useful being I'm not one of these people who like to BD all month long! LOL! They are pretty cheap too.....