[T]he multilateral treaties, conventions and agreements of an economic or technical character enumerated below … shall alone be applied as between Germany and those of the Allied and Associated Powers party thereto:
. . . .
(22) Convention of November 16 and 19, 1885, regarding the establishment of a concert pitch.
I was about to joke how that probably contributed to WWII, but it turns out they had already pushed it into Germany and Italy 30 years before WWI.
But, humm… Unless it was Japan’s reason to join.