From Boeing, "Many AOA indicators used in the past have been of the "normalized" type, where AOA is shown in arbitrary units and scaled so that zero load factor is shown as an AOA of zero and stall is shown as an AOA of one. Normalized AOA on a commercial jetliner would require that Mach number be introduced into the calculation of AOA because stall AOA and buffet margins are a function of Mach number." Except in our case it's 0-30 rather than 0-1.
http://www.boeing.com/commercial/aeromagazine/aero_12/attack_story.html