(a) The datum for the establishment of grades in the village is hereby established as the same as the Chicago city datum as established by the trustees of the Illinois And Michigan Canal, in 1847, which datum was measured from the plane of low water in Lake Michigan in that year.
(b) The standard elevation of the notch cut in the water table at the northwest corner of the three-story brick building at the southwest corner of Deerfield and Waukegan Roads, shall be and is hereby established at 112.496 feet above datum, which elevation shall be the bench from which all village grades and benches shall be established. (1963 Code § 10.603)