Units of measurement used outside UK and US

Hi all, I'm having some discussion with fellow enthusiasts on
the measurement of suction including the units of measurement. The
usual traditional units used for wind pressure and suction for organs
and player pianos in the UK and the US (and probably in some other
countries) are inches of water gauge, but what units are used by organ
and player technicians elsewhere, i.e., where inches are not used
or are no longer used?

I'm thinking especially of mainland Europe. For example, how are
suction levels for (German) Welte-Mignon reproducing pianos specified
in the original technical manuals (if they are specified at all)?

Just to avoid any confusion, as an engineer I'm familiar with
the various SI and non-SI units used in industry, academia and more
generally (pascal, bar, millibar, Torr, atmospheres, psi etc.), but I'm
wishing to find out about the units used traditionally in the player
piano and organ world where scientific units may not prevail, and in
places where inches aren't in common use.

Neither am I referring to the physical device (water manometer, bourdon
gauge, digital manometer, etc.) used for measurement either, though
obviously "inches of water gauge" originally referred to a water
manometer. Any information would be greatly appreciated.

Kind regards,

Arthur Jones
Nottingham, in the East Midlands of the UK