Complications Explained: Power Reserve Indicator

The power reserve indicator is another complication that can be found on a watch. Mechanical watches are powered by a coiled spring known as a mainspring. When you wind your mechanical watch or the rotor of your automatic watch spins, you are winding up the mainspring. When the coil unwinds, energy is released into the watch. The power reserve of your watch is how long the watch has until the coil is completed unwound.

The earliest power reserve indicators were found on marine chronometers and railroad pocket watches. But the first pocket watch to feature a power reserve indicator was a prototype watch from 1933 manufactured by Breguet. The first production watch with a power reserve indicator was the Jaeger LeCoultre Powermatic from 1948. It ran off the caliber 481. The watch has a cutout on the dial at 12 o’clock and a coloured wheel that indicates how much power reserve is left.

There are various ways a power reserve indicator can be displayed. Many watches have cut outs like the Powermatic has. Others have a power reserve hand that increases and decreases as the power reserve changes. One of our favourites is on the MB&F Legacy Machine 1 where it is a vertical power reserve indicator that takes its inspiration from the marine sextant.

Enjoy!