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Historical Mapping Photographs
A Johnson Elevation Meter mounted in a four-wheel-drive GMC Suburban 1960 model K1001 truck. The slope angle of the road was measured by a sensitive electronic pendulum, and the distance was measured by the fifth wheel. An onboard computer solved for the difference in elevation ten times per second. In areas of moderate relief with an adequate net of relatively smooth roads, these instruments were capable of establishing elevations within 2 feet while traveling at speeds approaching 30 miles per hour.
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