Geodetic Digital Leveling Survey - Spirit Leveling

Geodetic Leveling (or "spirit leveling") is a classic technique in which the height difference between two separated vertical rods is determined with a leveled (with respect to the local plumb line) viewfinder. The height between two bench marks is determined be keeping track of the accumulated difference as the leveling party traverses from bench mark to bench mark. Leveling is an extremely precise relative measurement, routinely achieving uncertainties of 0.7 mm/√km.

Leveling provides height differences between each bench mark in the GSVS. These heights, "weighted" by the gravity values at each benchmark, are used to determine the vertical undulations of the geoid. These undulations, divided by the horizontal distance (from GPS) provide slopes.