Glossary · Regulation
Equation of time
The varying difference between apparent solar time and mean (clock) time through the year.
Explanation
The equation of time is the difference between apparent solar time (sundial time) and mean time kept by clocks, varying through the year by up to about 16 minutes fast or slow. It results from the earth's elliptical orbit and axial tilt. Watches with an equation display use a kidney-shaped annual cam; historically, equation tables were pasted into watch cases and clock doors.
In the object catalogue
Catalogued objects whose own source record mentions “Equation of time”. The quoted line shows where; it is the seller’s or museum’s wording, not independent verification.
Pocket watch
Paul Ditisheim Astronomical Precision Pocket Watch No. 13784
“This astronomical precision pocket watch by Paul Ditisheim features a 61mm 18ct yellow gold Empire case with a reeded band. The white enamel multi-piece dial displays Arabic num…”
Tool
Ansonia Sunwatch (pocket compass dial)
“According to the Science Museum Group, this pocket horizontal sundial known as the Sunwatch was manufactured between 1922 and 1939 in New York county by the Ansonia Clock Compan…”
Wristwatch
Breguet Marine Tourbillon Équation Marchante, Reference 5887PT/Y2/9WV
“This Breguet Marine Tourbillon Équation Marchante is a platinum perpetual calendar tourbillon wristwatch dating to circa 2022. It features a blue wave-pattern guilloché dial wit…”
Clock
Breguet et Fils / George Daniels No. 3225 pendule à trois roues skeleton clock
“This weight-driven pendule à trois roues skeleton timepiece, numbered 3225, was completed in 1968 by George Daniels and officially registered by Breguet proprietor George Brown.…”
Clock
Musée International d'Horlogerie Breguet 'À Trois Roues' reproduction pendulum clock
“Dial Displays: Gregorian and Republican calendars, equation of time, seconds”
Wristwatch
Franck Muller Cintrée Curvex Perpetual Calendar Reference 6850 QPE
“This Franck Muller wristwatch, identified as a Cintrée Curvex Perpetual Calendar reference 6850 QPE, was produced in 2001. The tonneau-shaped case is constructed from 18K white …”