Why we track equation of time

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Why we track equation of time

Post by koimaster » December 13th 2020, 3:52am

Like the minute repeater, tourbillon and the perpetual calendar, the equation of time is a rare and valued complication. True, it is an arcane function that neither chimes the hours, nor fights the effects of gravity, but it is rooted in the history of watchmaking and is therefore meaningful for aficionados.

The equation of time tells us the solar time - the amount of time it takes the sun to return to its original position in the sky each day, which on average does not vary significantly from real time (no more than 16 minutes). For practical reasons, man has divided each year into 365 and a quarter days, each day into 24 hours, and the hours into 60 minutes each. However, because Earth’s orbit is elliptical rather than circular, the time in relation to the sun varies daily. It is exactly twenty-four hours long on only four days: April 15th, June 14th, September 1st and December 24th. Because these variations occur identically on the same dates, they can be programmed into a watch movement by means of a simple cam making one complete rotation a year. The cam is usually linked directly to a perpetual calendar, so the display of the equation of time always corresponds to the current date.

Of the two ways to display the equation of time, the method most true to its name is the inclusion of a subsidiary dial or arc, graduated from -16 to +14 minutes to indicate how many minutes you should add or subtract from mean time to get the actual solar time - in other words, it’s an equation or calculation. A recent example of this is the Panerai Radiomir 1940 and Luminor 1950 Equation of Time special editions, introduced at the SIHH in 2015. Both use linear scales rather than an arc to show the variation, placing it along the bottom of the dial where Panerai often places a power reserve indicator.

https://journal.hautehorlogerie.org/en/ ... n-of-time/


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