The Clearplan Easy ovulation prediction kit monitors the amount of luteinizing hormone (LH) in your urine. Normally, the level of LH will suddenly increase (known as the LH surge) near the middle of your menstrual cycle causing the release of an egg from the ovary between 20 and 44 hours later. This whole process is known as ovulation.
Clearplan Easy uses a technique known as EMIT, enzyme-multiplied immunoassay technique, to detect the surge in LH. This is a relatively new idea which uses monoclonal antibody technology to detect very small quantities of a protein in the urine.
For more information on EMIT and ELISA