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The Encyclopedia of Horology

Complication · Display

Portable Sundial

Partially verified

A portable instrument telling time from the sun's position.

Definition

A portable instrument telling time from the sun's position.

Historical origin

Portable sundials, including diptych and ring dials, were the practical portable timekeepers before mechanical watches became reliable and affordable.

How it works

A gnomon casts a shadow across an hour scale drawn for a specific latitude; some designs are adjustable for latitude.

Correct use requires orientation to true north, which is why many portable dials incorporate a compass.

Pocket watch context

Portable dials were carried alongside early watches, and were used to check them.

Wristwatch context

Not a wristwatch complication, but the direct ancestor of portable timekeeping.

Clock context

Fixed sundials remain the reference against which early mechanical clocks were set.

Identification

  • A gnomon and an hour scale, frequently with a latitude list or an adjustable arc

Servicing notes

Conservation of a historic dial is museum work: original engraving, gilding and hinges are the object's value, and cleaning removes evidence.

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

Diagram

subsidiary secondschapter ringminute and hour hands
Schematic: dial layout and hands. 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.