Clearblue pinpoints your 2 most fertile days when trying for a baby. Digital Ovulation test (10) and over 99% accurate. The simple urine tests are proven to be over 99% accurate at detecting the LH surge. They are 2x more accurate than calendar methods. Detects the surge in a fertility hormone (LH), which occurs just before ovulation. Make love at any time in the next 48 hours after your first ‘smiley face’ to maximise your chances of getting pregnant naturally.