Credits: Article and images by Ashton Tracy @ Quill & Pad. See the original article here - https://quillandpad.com/2024/03/09/its-a-date-taking-a-closer-look-at-the-most-popular-complication-of-them-all-the-calendar-2/
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Instantaneous calendar
The instantaneous style is the most sophisticated of the three as it allows date change to take place exactly at midnight.
It uses a spring to accumulate energy over a period of time and then releases that energy at midnight, causing an abrupt snap that advances the date disk one tooth forward.
Rapid date change: the mechanics
The rapid-date change can be categorized into two camps, then boiled down further into two more subcategories.
The first is a mechanism that uses an independent corrector, usually on the side of the case. The second is a style that is incorporated into the winding stem.
The two sub-categories that follow are those with a safety device and those without.
Rapid-date change corrector
Rapid-date change correctors are usually found in complicated watches that display more than just the date. They are commonly seen in triple calendar movements, but really any watch can make use of one.
Easily recognized as a small push piece on the outside of the case, correctors are very simple mechanisms to repair and operate. You simply press the corrector downward and the date advances one increment. The push piece will then spring back once depressed, ready to perform its service all over again.
The push piece itself is connected to a lever inside the movement, which in turn acts against a toothed star wheel that advances one tooth forward. The star wheel can either have the hand directly attached to its arbor or it can transfer power to another wheel down the line.
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Credits: Article and images by Ashton Tracy @ Quill & Pad. See the original article here - https://quillandpad.com/2024/03/09/its-a-date-taking-a-closer-look-at-the-most-popular-complication-of-them-all-the-calendar-2/