The nature of the adjustable tool-machines (points a1, a2, a3, a4 below), the specific functional temperature of each piece (point b he low) as well as the roughness over the pair pieces surface (point c)i can drastically distort (falsify) the relation between the contact values at their fit. In the present study, we discuss the accurate measurements by establishing the ideal values which come from statistical and methodological estimations (calculus).