The complicated tables and timely calculations required for celestial navigation were effective at sea. However, the speed of airplanes presented new problems and inspired Weems' tireless pursuit to simplify navigational techniques.
The Weems System required two shots of the sun with a modified sextant, an accurate time reading from the second setting watch, and referencing of the tables in the Line of Positions book - a revolutionary method for navigation at the speed of flight.
Weems invented the Second Setting Watch - a watch that would help navigators find Greenwich Mean Time - a critical step. The final design allowed a navigator to read an accurate time directly from the watch face.
When you set a watch, you can adjust the hour and minute hands, but the second hand sweeps on irrevocably. To the layman it is not important if his watch is twenty seconds off. To the navigator, it can be a matter of life or death. So navigators, when they synchronized their watches with observatory time, used to make note of how many seconds their sweep hand was off. This factor, plus or minus, had to be figured for every calculation they made on a voyage. Weems mounted a movable rim on his watch, marked the sixty seconds on it and, since he was unable to adjust the second hand to the watch face, he simply adjusted the face to the hand.
The Line of Position Book offered the navigator extensive charts of pre-calculated positions. The air navigator could simply and quickly look up the positions, instead of doing extensive complicated calculations.
Weems modified a sextant to operate independent of the horizon to facilitate navigation in the air, where the horizon is not visible. This innovation provided the foundation for the invention, more than a decade later, of the Link Bubble sextant.
