above sea level

Yesterday I learned an interesting fact and it seems that using above sea level as a meaurement of land height can lead to costly mistakes if the sea is not stipulated . I t seems that the Swiss take the Mediterranean as their reference point whereas just across the border, the Germans refer to the North Sea. Apparently these two seas have a difference in level of about 27 centimetres, a fact which showed up quite clearly when the Swiss and the Germans each from their respective side of the Rhine, decided to build a bridge to connect with each other at Laufenburg. Oh dear , what a shock when they reached the middle over the Rhine and found a gap of 27 centimetres.That's hi-tech engineering for you . xxx