Edith Lackner's 1937 Longines Weems Second-Setting Watch (2)
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Lt. Philip Weems' Second-Setting Navigation Watch 

Early aviators on long flights sometimes faced great danger because they could not figure out exactly where they were. “Fixing” position over water, in the dark, or in poor weather was difficult.  With speeds of 200 - 300 miles per hour, a slight error in timekeeping when calculating one’s position could have disastrous consequences, and take the pilot many miles off-course.  A pilot needed to set a watch precisely to the exact second, by synchronizing it to a land- or ship-based GMT radio time signal

"The Weems bezel is universally regarded as one of the essential features on early pilots’ watches. It was invented in the early 1930s by Lt. Commander Phillip Van Horn Weems. Working for the US Naval Academy in Annapolis, Weems was brilliantly ingenious, and many of his techniques by which a pilot could relate his position to that of the stars while flying at night are still in use as standards today. Charles Lindbergh studied under Weems before making his historic 1927 trans-Atlantic flight in the Spirit of St. Louis. 

Today,  time synchronization is achieved via GPS.  When Weems devised his invention, even a reliable hacking movement (stopping the seconds hand by pulling the winding crown out) was not widely available. Weems’ solution to the seconds synchronization problem was a far better one, achieved by having a rotating bezel, calibrated in segments between 0 and 60. Therefore, at any time, the bezel could be turned to align its vertical 0 position to synchronize with the radio time signals broadcast.

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