The equation of time is the difference between time as read from a sundial and time as read from a clock or watch (also called solar time).

Due to the elliptical orbit of the earth the two times only match on April 15, June 14, September 1 and Dec 24th. On all other days, the deviation reaches from minus 16 minutes 23 seconds (4 November) to plus 14 minutes 22 seconds (on February 11).

A manufacturer who specializes particularly in wristwatches with equation of time display is Martin Braun. His model Notos also offers the additional complication of the display of the declination.

• Sunrise and sunset
• Sidereal time