The Mechanical Watch

The mechanical watch is one of the few remaining practical, day-to-day items that has remained unchanged in many ways since its inception hundreds of years ago. Of course, materials and production methods have come a long way since the seventeenth century, but if you crack open a modern mechanical watch, you'll find something that looks a lot like what you'd find if you peered inside a watch built 150 years ago. And this is true whether you're looking at an $80 Seiko or an $800,000 Patek Phillipe.

So what is that you'd be looking at inside one of these watches? Once you've stripped away the complications, you'll find the same basic structure in every mechanical watch: a mainspring powering a going gear train that is regulated by an escapement.

Alright, that may sound confusing, but it's just three basic systems. The mainspring is a long metal spring curled up inside a housing called a barrel. The wound spring slowly releases its tension, rotating the barrel, which in turn powers the escapement.

The escapement is where all the drama happens. Put simply, the escapement controls how quickly the barrel drives the gears, which is how time is kept. A large wheel with another spring spins back and forth, and is attached to a pallet fork holding the gears in place. Each time the wheel turns, the fork jumps to the opposite side, allowing the gears to make one "tick." Most modern watches beat away at about 4Hz, though some go much, much faster.

This 1949 video from Hamilton may seem a little corny, but it is probably the most straightforward explanation of a mechanical watch around.
On top of this base structure, with the help of some pretty complicated math and a few more gears, you can add a stopwatch function, calendar functions, moophase indicators, and almost any other time-based indication you can think of, all powered by the same barrel, gears, and escapement.

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Source From: http://gizmodo.com