This clockface shows your current biorhythm chart and stats.

Biorhythm theory started in the late 19th century, and holds that our physical, emotional and intellectual abilities vary in regular cycles. Some people advocate a fourth cycle for intuition. Days when the cycles transition from positive to negative, or vice versa, are said to be critical (ie, especially bad).

This clockface graphs your biorhythms for 2+ weeks ahead, and a few days previously. Today’s date is highlighted in grey. X indicates a critical value.

Versa 1/2/Lite: To change settings, long-touch the screen or press one of the right side buttons. You can change the date of birth used, which lets you see biorhythms for other people.

Versa 3/Sense: To change settings, use the Fitbit app on your phone.

The app also displays one of the standard Fitbit activity measures: energy, steps, distance, active time (AZM on Versa 3/Sense), elevation, and heart rate. Touch the screen to cycle through them.

On Versa 2/3/Sense, Biorhythm has an Always-On Display mode.

Cost: $1+tax. If you buy the Biorhythm Bundle, you won’t pay any more and you’ll get an app version as well (better for occasional use).