The National Geodetic Vertical Datum of 1929 (NGVD 29) is a reference system used in the United States to measure elevations. Established to provide a consistent baseline for elevation data, it was created by surveying benchmarks across the country. These benchmarks serve as points of reference for various applications, including construction, mapping, and floodplain management. NGVD 29 is based on mean sea level from the year 1929, which means it uses historical sea level data to define elevation points. Although it has been largely replaced by the more modern North American Vertical Datum of 1988 (NAVD 88), NGVD 29 remains important for historical data comparisons and certain engineering projects.