Clearblue Digital Ovulation Test is an easy to use digital test that is fast, proven 99% accurate and easy to read. Results are in just 3 minutes, telling you the best days in which to conceive your baby naturally. Clearblue Digital Ovulation Test works by detecting an increase (surge) in the hormone called Luteinising Hormone (LH) in your urine. This LH surge occurs prior to the release of an egg from your ovaries - a process known as ovulation. You are at your most fertile on the day your LH surge is detected and the day after.