I don't know...seems like it should appear like another 10 feet above the bridgehouse. The Mezz is 34' from the Plaza and another 4 feet from the road level on the East side. The bridgehouse can't be more than 20'.
Flaccer - that 675' height is in fact from the Plaza. which is 31' 3" above the Chicago City Datum.
https://commons.wikimedia.org/wiki/F...City_Datum.jpg
"The City Datum is hereby established as a plane 17.640 feet below the bench mark cut on top of the bottom stone of the granite base at the southeast corner of the Northern Trust Company bank building at the northwest corner of South Lasalle Street and West Monroe Street"