The typical ovulation tests have 2 lines: the test line (T), and the control line (C). The T/C ratio simply compares the color intensity of the T line to the color intensity of the C line. The change in the T/C ratio indicates the increase or decrease of LH levels in the tested urine. (Test line as dark as the control line = 1. Test line lighter than control = less than 1. Test line darker than control = greater than 1.)

T/C ratio has positive correlation with LH level so its change can reflect the LH level change. Therefore T/C ratio is used to measure the increase or decrease of LH level in urine.

When looking for your LH peak, you are aiming for a ratio of 1.0, when the test line is as dark as the control line. A test line lighter than the control line will be less than 1.0. A test line darker than the control line will be higher than 1.0.