Wrong measurement
I have attached 3 pics showing the measurement sequence of a simple round part with 2 holes measuring 40mm and 47mm. The total width (external) of the part is 41mm. But measuring from inside each hole to outer faces we get wrong measurements or 14mm+28mm=42mm.
It should be 13,5+27,5=41mm because the hole 47 cuts from outer face and moves 7mm after the center of the part=20,5+7=>27.5mm and the hole 40mm cuts from 27.5 up to the outer face = 13.5mm.
