That MOUS system is the standard in the Netherlands and elsewhere for, among other things, plumbing points from the ground floor to as many floors as you want.
So that you can be sure that the base point and starting point on each floor are exactly the same to the mm and one above the other.
Meanwhile, the MOUS System is defacto the standard when it comes to plumbing main measuring points in buildings. And this is true not only here in the Netherlands, but also in a 'precise' country like Switzerland.
To ensure that the same reference points are used on several floors, the basic Mous points can be 'plumb' up through holes in the storey floors using a plumb laser. In existing buildings, holes are drilled/sawn in the storey floors; in new buildings, the storey floors can be saved in advance for the Mous system. Mou points are then present on each floor so that the rest of the floor can be plotted at that point with a Totalstation, so that on each floor walls etc. are exactly on top of each other, if desired.