The seating plane (1st datum S) and all the central terminal locations show that when straight line A (2nd datum A), which is obtained by the Least Squares Method, is used as the standard, fluctuation in the central location of the package for the length direction (D) is within ±0.10mm of the 2nd datum A.
See "Measuring method for Package Dimensions of BGA EIAJ ED-7304"
