Complication · Display
Power Reserve Indication
VerifiedA dial display, usually an arc or subsidiary dial with a hand, showing how much running time remains before the mainspring fully unwinds.
Definition
A dial display, usually an arc or subsidiary dial with a hand, showing how much running time remains before the mainspring fully unwinds.
Historical origin
Power reserve (also called 'up-and-down' in its earlier form) indications appear on marine chronometers and precision watches from the nineteenth century, developed to let the user or navigator know when winding was needed to avoid the watch stopping.
How it works
A differential or reduction gear train is taken from the mainspring barrel arbor, which rotates a fixed number of turns between fully wound and fully run down; this rotation is geared down to drive a hand across a scale marked from full to empty.
Because the barrel arbor's rotation count is fixed by the spring's length and the barrel's gearing, the power reserve mechanism must be calibrated specifically to the calibre's spring and barrel dimensions during design, not simply added generically.
In automatic watches the same principle applies, with the barrel continuing to be read even as the mainspring is topped up by the rotor, so the display constantly reflects the balance between winding input and the movement's ongoing consumption of stored energy.
Pocket watch context
Predecessor 'up-and-down' indicators were fitted to marine chronometers and some high-grade pocket watches to show winding state at a glance, especially useful before quick-set or automatic winding existed.
Wristwatch context
A common modern complication, particularly on manually wound watches, where it helps the wearer judge remaining running autonomy before the watch stops.
Identification
- An arc-shaped or subsidiary-dial gauge, usually marked in hours or as a fraction (e.g., full/half/empty)
- Distinct from a mainspring-tension indicator; power reserve reads elapsed running time, not spring torque directly
Servicing notes
The differential gearing must be correctly calibrated to the specific barrel and spring; incorrect reassembly after service can produce a reading that does not match actual remaining reserve, which should be corrected by a watchmaker familiar with the calibre.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- de Carle, D., Watch and Clock Encyclopedia
Where sources disagree, the disagreement is stated rather than resolved silently.