technically it's "electromechanical" but does not use GPS, WiFi, quartz, or atomic methods. To make thigns this accurate you need extremely good temperature compensation, close-to-frictionless bearings, run in a vacuum, use a pair of pendulums, etc.
When you reach that level of accuracy, you end up basically building a sensitive measurement device that is influenced by second and third order terms like subtle changes in the shape of the earth.
technically it's "electromechanical" but does not use GPS, WiFi, quartz, or atomic methods. To make thigns this accurate you need extremely good temperature compensation, close-to-frictionless bearings, run in a vacuum, use a pair of pendulums, etc.
When you reach that level of accuracy, you end up basically building a sensitive measurement device that is influenced by second and third order terms like subtle changes in the shape of the earth.