I work in print and we use our own GUI to create documents based on InDesign files, however the issue I'm having is that this one file has a font that uses -40 character spacing. I understand that these are in ems, so how would I go about translating that into mm which is what our GUI is using or can I change the settings in InDesign so that character spacing is shown in mm's or is that not how it works?
Any help would be greatly appreciated!
The whole reason for using a relative unit, like ems, for tracking and kerning is it adjusts as you change the size of the type to maintain the specified spacing. If you switch to an absolute unit and adjust the type size your glyphs will either drift apart or pile up on each other.
And I don't think anyone here can even begin to tell you how you might accomplish such a feat in your custom GUI.