The base or datum for the street and other levels of the Village is the level of Lake Michigan as approximately determined by the Village surveys in 1886 and is hereby established as the horizontal plane 95.35 feet below a rectangular bench mark in the concrete at the base of the iron flagpole on the Village green at Hillgrove Avenue near Lawn Avenue. Said bench mark is also 673.329 feet above mean sea level as determined by the United States Coast and Geodetic Survey in July, 1947 (said elevation being the preliminary field determination, subject to minor correction when adjusted or fitted to the national level net). (1997 Code)