Thanks for the jsfiddle. I think I understand what you mean. Cross-referencing this with how the new Inkscape saves files actually makes sense. By using width/height and viewBox you can define how user/px units are converted to physical units.
When I setup up Inkscape to use mm it does set with/height in mm and then the viewBox to the same dimensions (without units). This way it is implying the user/px units (e.g. all unitless dimensions in the file) are basically mm.
Previous versions of Inkscape would always safe in user/px units with an implied conversion of 90dpi, meaning a scaling factor of (25.4/90) to go from values in the file to mm. CorelDraw always uses 96dpi, Illustrator always 72dpi. I am not saying this makes sense. It's just how different authoring apps do it. If you want to use the file in a CNC machine you have to make sense of what the app meant when it uses unitless dimensions. When a file was edited with two different apps it very often is not possible to make a smart guess by some basic heuristics.
BTW: the CNC app I am working on is LasaurApp, part of an open source laser cutter called Lasersaur - http://lasersaur.com
When I setup up Inkscape to use mm it does set with/height in mm and then the viewBox to the same dimensions (without units). This way it is implying the user/px units (e.g. all unitless dimensions in the file) are basically mm.
Previous versions of Inkscape would always safe in user/px units with an implied conversion of 90dpi, meaning a scaling factor of (25.4/90) to go from values in the file to mm. CorelDraw always uses 96dpi, Illustrator always 72dpi. I am not saying this makes sense. It's just how different authoring apps do it. If you want to use the file in a CNC machine you have to make sense of what the app meant when it uses unitless dimensions. When a file was edited with two different apps it very often is not possible to make a smart guess by some basic heuristics.
BTW: the CNC app I am working on is LasaurApp, part of an open source laser cutter called Lasersaur - http://lasersaur.com