The U.S. Department of the Interior  used a device known as a Johnson Elevation Meter Machine an was mounted on this 1960 GMC Suburban model K1001 four-wheel-drive suburban. The slope/angle of the road was measured by a sensitive electronic pendulum, and the distance was measured by that fifth wheel. Yes there was even an onboard computer that solved equations 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 which made for a great vehicle to help map out the U.S.