The Clearblue Advanced Digital Ovulation Test is a breakthrough: unlike all other ovulation tests which only detect one hormone, not only does it detect the rise in luteinizing hormone (LH), it also monitors the level of another key fertility hormone, estrogen, which increases in the days before the LH surge. By tracking these 2 key hormones, this test is able to typically identify 4 fertile days leading up to, and including the day of ovulation, twice as many as any other ovulation test. Unlike strip and cassette tests which can be fragile and hard to read, the digital ovulation test is easy to use and gives you clear results showing a smiley face on your most fertile days. The number and position of the fertile days may vary from woman to woman and from cycle to cycle. Your results will be personal to you and some women may see more or less High Fertility days.