question about advanced digital ovulation test

Hello, I bought clearblue advanced digital ovulation test, 10 tests with one monitor inside, I am going to try them this month, but I have a question, how many times you can use monitor (how many times you can see ovulation - smiley face with each monitor)? I read comments today that one lady used monitor last month and got smiley face, she used the same monitor this month she didn't get smiley face and also used new monitor -( tested both at the same time) and did get smiley face so she was confused why, and another lady left comment, that you can use monitor only once if you get smiley face you cannot reuse it again, it memorize ovulation and cannot be used again, you have to use new monitor - is it true?