Photo: Mark Avino, Smithsonian
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. This was one of his personal navigation watches. Sidereal refers to the watch running on a celestial day (about 23 hours, 56 minutes), rather than the 24 hour solar day. This object will be part of the Time and Navigation exhibit opening in April 2013.
Image Number: WEB12700-2013
