Inside: How a Movement Works

Open the caseback of a mechanical watch and you'll find a tiny machine with no battery, no circuitry — just springs, gears, and levers. Every mechanical movement, from a $200 Seiko to a $200,000 Patek, works on the same chain of five ideas.

The power chain

• 1. Mainspring — a coiled ribbon of steel in a barrel. This is the fuel tank; winding the crown (or a rotor) coils it tight.
• 2. Gear train — a series of wheels that carries power from the barrel across the movement, gearing it up so the hands turn at the right speeds.
• 3. Escape wheel — the last gear, with distinctive hooked teeth. It wants to spin freely, but…
• 4. Pallet fork — a tiny anchor-shaped lever that locks and unlocks the escape wheel one tooth at a time. Each unlock is one tick.
• 5. Balance wheel + hairspring — the pendulum. It swings back and forth at a fixed tempo, flicking the pallet fork on every pass. This sets the pace of the whole watch.

Watch the exchange: the balance wheel swings, knocks the pallet fork across, and the escape wheel jumps forward exactly one tooth — giving the balance wheel a tiny push in return to keep it swinging. That push-per-swing bargain is the entire secret of mechanical timekeeping, essentially unchanged since the 1750s.

The numbers you'll hear

A modern movement typically beats at 28,800 vibrations per hour (8 ticks per second — written as 4 Hz), runs about 40–70 hours on a full wind (the power reserve), and rides on 17–25 jewels — synthetic rubies used as nearly frictionless bearings at the busiest pivots.

A healthy mechanical watch keeps time to within a few seconds a day. A chronometer-certified one (COSC) is officially tested to −4/+6 seconds per day. Quartz beats them all by a mile — but as we'll see, accuracy was never really the point.