Its been awhile for me with any Mitutotyo software but I believe your max and min values are based upon your current reference frame and the flatness call-out is based upon a least squares best fit plane then the max and min points based upon that generated plane.

Timothy A. Schroeder
Supervisor- CMMs, Gearlab, and Gage Inspection
Rolls-Royce Corporation
P.O. Box 420, Speed Code R29A
Indianapolis, In 46206
Tel: (317)230-5914