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The Encyclopedia of Horology

Complication · Display

Power Reserve Indication

Partially verified

An indicator showing how much mainspring energy remains.

Definition

An indicator showing how much mainspring energy remains.

Historical origin

Developed for marine chronometers and precision watches, where running down unnoticed was a serious risk.

How it works

A differential gear compares winding and running motion, driving a hand or disc that falls as the spring unwinds.

In chronometers the same indication is traditionally called an up-and-down dial.

Pocket watch context

Standard on marine chronometers and deck watches, and found in high-grade pocket watches.

Wristwatch context

Used in both dress and tool watches, and especially in long-power-reserve calibres.

Identification

  • A subsidiary scale marked with a range rather than time
  • Traditionally labelled up and down on chronometers

Servicing notes

This is specialist work. Levers, springs and cam profiles in complicated work are calibre-specific, and incorrect reassembly commonly damages parts that cannot be bought. Refer the movement to a watchmaker experienced with this mechanism.

General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.

Diagram

coiled mainspring inside the barrelbarrel teeth driving the trainarbor and hook
Schematic: mainspring and barrel. An outline schematic drawn to show the arrangement of the parts discussed here. It is not a dimensioned working drawing and does not depict a particular maker's calibre.

Sources & references

  1. de Carle, D., Watch and Clock Encyclopedia
  2. Britten, F. J., Old Clocks and Watches and Their Makers
  3. Horological Journal (British Horological Institute), technical articles

Where sources disagree, the disagreement is stated rather than resolved silently.