40-hour power reserve movement

What is a power reserve?

Power Reserve refers to the running time of a fully wound mechanical watch (manual-wind or automatic). For example, if you fully wind your watch and place it on your dresser, how long before it stops running and needs to be wound again - that is the power reserve.

What does power reserve mean on a watch?

"Power reserve", then, refers to the available energy stored in a watch's mainspring. While the watch runs, the spring gradually unwinds, until all the power is spent and the watch stops or is wound up again. Over time, watches have evolved to provide typically around 40-50 hours of power, enough for two days or so.

How long does the power reserve last on a watch?

The mainspring gets wound up, then as the watch runs down (displaying the time), it eventually stops when all of the tension (stored energy) is released from the spring. Until recently, the most common length of power reserve was around ~38 hours (an ETA 2824-2 for example) or 46 hours (an ETA/Unitas 6497-1).

How long should a mainspring power reserve be?

Until recently, the most common length of power reserve was around ~38 hours (an ETA 2824-2 for example) or 46 hours (an ETA/Unitas 6497-1). With advances in materials and design of mainsprings and mainspring barrels, it has become a trend to increase the power reserve as much as possible.

What is a power reserve in a clock?

Previous clocks had used simple weights on pulleys, or the flow of water through a water wheel to provide power. Springs were much more effective because they could be condensed into a small space, allowing timekeeping mechanisms to shrink to portable sizes. "Power reserve", then, refers to the available energy stored in a watch's mainspring.

How long can you leave a watch without a power reserve?

The longer the power reserve, the longer you can leave your watch between wearing or winding – regardless of how much power reserve is left when you leave it. How much PR you “need” depends on a) whether you give a damn and b) your watch wearing habits. Generally speaking, most mechanical watches have a power reserve between 40 and 50 hours.