Technical: The Minute Repeater

Picture the scene: it’s mid-winter, and the grey sky is fading to black as a bleak afternoon becomes an even bleaker evening. You want to know what the time is, but there are no lights to switch on—because it’s the mid-eighteenth century—and the dim firelight is too low to read by. What do you do? You check your repeater watch, of course. Pull the lever, listen to the chimes. Now you know what the time is. Sounds simple when it’s put like that, but it’s not—it’s really, really not.

Piaget’s Emperador Coussin Ultra-Thin Minute Repeater houses the beautiful calibre 1290P. The minute repeater mechanism is reversed so it can be viewed under the dial

The first repeating mechanism is found, unsurprisingly, in a clock. Invented by the Reverend Edward Barlow in the late 1600s, it was a complex and expensive design that wasn’t replicated in a pocket watch until the end of the century. Famed British watchmaker Daniel Quare acquired the first patent for a repeater complication in a pocket watch, an impressive compaction of the bells, hammers and striking works. The pocket watch movements were still large, and a wrist-watch sized minute-repeater movement didn’t see the light of day until 1892, in a watch by Louis Brandt.

The stack of snail cams in the centre runs off the hour and minute hands. The hour cam has twelve steps, the quarter four and the minute fourteen per quarter

Repeater watches come in several variations, each one more complex than the last. The first and most simple is the hour repeater, which chimes the hours on command. Then comes the quarter repeater, which chimes the hours and, with a different tone, the quarters. A five-minute repeater follows, chiming the hours and five-minute intervals in succession. A minute repeater is the most impressive of all repeaters, chiming the hours, then the quarters and finally the minutes. A minute repeater with an hour or quarter striking mechanism also exists, and is known as a grande sonnerie.

A flywheel works off centrifugal force to regulate the speed of the minute repeater’s operation, much like a balance wheel regulates the timing of the movement

There’s a reason minute-repeater watches take two to three hundred hours to assemble: the striking mechanism alone can have upwards of a hundred parts in its makeup. Its chime all begins at the lever, the case-mounted actuator for the mechanism. Originally, repeater watches drew power from the mainspring, but the power demand has since necessitated the addition of a separate spring, wound by the sliding lever. Like the adaptation of the older style bells to the current wire gongs, the spring mechanism was introduced by Abraham-Louis Breguet, inventor of the tourbillon.

The rake triggers the striking of the hammers on the gongs, each tooth corresponding to an individual strike. The snail cams determine how much of the rake is used

Three snail cams—one for the hours, one for the quarters and one for the minutes—rotate with the hour and minute hands freely when the repeater mechanism is not operating. When the lever is pulled, a partial gear (called a rack) is engaged with the hour snail cam via a lever. The steps on the snail cam determine how many of the teeth on the rack pass by the striking mechanism, each one causing the hammer to strike the gong. The process is repeated for the quarter cam and rack (which has two layers to engage both hammers), and then the minute cam and rack follow. A centrifugal governor regulates the speed of the mechanism.

The gongs themselves are made of thick wire, tuned to produce the required tone and volume. Older minute repeaters used a less space-efficient bell instead

It’s easy to see why the minute repeater is considered king among complications. Developed over several centuries, the amount of engineering and mathematical constraints the design has overcome is astonishing. The quiet chimes of a minute repeater may not have much of a place in the modern world, but in the heart of an enthusiast they ring clear and true.

The hammers strike the gongs to produce the chime, powered by a dedicated spring. The low gong indicates the hours, low and high together the quarters, and high the minutes