Clearblue Digital Ovulation Test detects the rise of the ovulation hormone LH (luteinizing hormone) 24-36 hours prior to ovulation and identifies the 2 best days to conceive in a given cycle.Your ovulation period is vital to keep track of in order to have a successful conception. The Ovulation Test from Clearblue helps you maximize your chances of getting pregnant by keeping track of the two hormones and your high/peak fertile days.