Analogue Air Position Indicator 21 of 51
This unit is from UK wartime aircraft, and computed an aircraft's latitude and longitude using an entirely mechanical (analogue) process, involving integration, sines and cosines.
The current speed and direction were fed in on servo-motors on the right of this photograph.
The speed was split mechanically into sine and cosine components for latitude and longitude changes, and integrated to give the current position.
The longitude calculation also needed an inverse "cosine" component (longitude changes more quickly nearer the poles proportional to the cosine of the latitude). The mechanical process would, of course, have failed near the north or south poles.
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