The benchmark or base as a starting point from which the grades of all the streets in the city shall be established, shall be the top of a piece of steel rail about three feet long, set in the ground at the common center of Fir and First Streets, the top of said iron post being about eight inches below the present surface of the ground, and at an assumed elevation of ten feet prepared by F. M. Lane, which said plat or profile is now on file in the office of the city clerk-treasurer. Whenever the city council establishes a grade on any of the streets of the city, the elevation shall be computed from the benchmark thereby established, and the same shall commence with the number of feet or inches above or below said benchmark. (Ord. 64 § 1, 1894).