Measuring the World
Why Elevation Follows Gravity: The Geoid Beneath Every Height
GNSS measures height above a mathematical ellipsoid, but practical elevation depends on gravity, the geoid, and a physical definition of level.
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Tag: Gravity
Reports, histories, and working notes filed under this subject.
Measuring the World
Measuring the Earth–Moon System: Lunar Laser Ranging and Millimeter Geodesy
How Apollo-era retroreflectors let observatories measure the Moon, test gravity, and strengthen lunar reference frames.
Measuring the World
Surveying the Highest Peak, Part 3: GPS, Geoids, Snow, and the Modern Height of Everest
Why modern Everest measurements depend on GNSS, gravity, snow depth, reference frames, and a clear definition of height.
Measuring the World
Finding Level: From Water Levels and Spirit Bubbles to Digital Heights
Establishing height has always required a definition of level, a reliable sight line, and a path of observations strong enough to reveal accumulated error.