It is possible to globally switch between these units for display purposes, but it would be desirable in some places to actually have them shown in parallel:
the measurement bar at the bottom would be nice to show both units without global switch.
Some input fields (e.g. text size, hole diameter..) should provide a way to switch between the units (and possibly mouse-over show the other unit). Each field should remember in which unit it was originally entered to always present in that unit by default (because the alternatives often have too many decimal places...)
It is possible to globally switch between these units for display purposes, but it would be desirable in some places to actually have them shown in parallel: