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Ah, many thanks, could not find the exact term to what I was refering in the previous post as "calibrating tiles in metrology"

They indeed were what I had in mind when I developped my first...

All right people, thanks to all of your wonderful contributions, and for the sake of correct scientific behaviour, which means reviewing your hypothesis, let me propose another, probably more...

If you want to get scientific on the issue :
when two surfaces are flat enough, particles from both surfaces tend to attract each other, pretty much the same way a Gecko can adhere ton any surface....