Just add 3 drops of urine to the Test Cassette and wait 3 minutes. If the Test Line (T) is darker than the Reference Line (R) you will know that ovulation will probably occur within 40 hours. Over 99% accurate in laboratory studies and greater than 96% accurate in consumer studies DirectionsOne easy step after collecting urine; simply add urine and read. Store at room temperature 15-30 C (59-86 F). WarningsNot for internal use. Do not freeze. Keep out of reach of children.