When you ovulated

Ovulation lasts a few hours and produces almost nothing you can feel, which is why calendar-based estimates can miss the actual timing of ovulation. What it does leave behind is heat. Once the egg is released the empty follicle starts producing progesterone, and progesterone resets the body’s thermostat upward, so your overnight temperature steps up within about a day and stays up until your next period.

Reading that step from the finger, the Ultrahuman Ring agreed with the reference test 92.9% of the time across 22 women, and 91.7% of the days it flagged turned out to be right.

The reference reads estrogen, LH, FSH and progesterone rather than the luteinising hormone surge alone. Reading several metabolites is the more accurate of the two ways to pin ovulation, so the Ring was checked against the harder standard.