Longines-Wittnauer Weems Second-Setting Watch Standard Model

Before 1927, watches used with sextants for celestial sightings could only be set to the minute. A watch error of 30 seconds caused a navigational error of up to 12 kilometers (7 miles).

In 1927, P. V. H. Weems devised a watch with an adjustable second hand that could be set using radio time signals. These examples were his personal navigation watches. 

Caption:
For use with radio time signals.
Type: Artifact
Image Date: February 8, 2013
Credit: National Air and Space Museum, Smithsonian Institution
Origin: National Air and Space Museum, Smithsonian Institution
Creator: Mark Avino
NASM2013-00429
Navigation Methods
 
For use with radio time signals.
For use with radio time signals.