The disk showing the equinoxes and solstices, as well as where the Sun is in the signs of the Zodiac, is just under the date display. The equinoxes and solstices mark the transitions between the seasons. A solstice occurs when the tilt of the Earth’s axis is most extreme relative to the Sun (specifically, when the Sun is directly overhead at the Tropic of Cancer or Tropic of Capricorn, which are the southernmost and northernmost circles of latitude where it’s possible for the Sun to be directly overhead at some point during the year). The equinoxes occur at those two times in the year when the tilt of the Earth’s axis is vertical relative to the Sun.

The Equation of Time is the difference between a mean solar day of 24 hours, and an actual solar day, which thanks to the tilt of the Earth’s axis, and the eccentricity of its orbit, can vary by as much as −14 minutes and 15 seconds, to +16 minutes, 25 seconds, at various points during the year. Normally, the Equation of Time is encoded on a kidney shaped cam that rotates once per year. Typically, the cam is contacted by a feeler on a lever that “reads” the position of the cam, and causes a hand to shift position that shows the plus or minus deviation from a mean solar day.