Exporting SVG in mm instead of px in AI

I am trying to export my vector graphics as SVG. Inside Adobe Illustrator everything is just right, measured in mm. But when I use the "save as" option it always converts it to px (scale factor around 1.25) which leads to heavy rounding errors and I want to use it for a CNC where accuracy matters.

So is there a option I am missing to stop it from scaling or a adjustable export scaling factor?

Or should I use another software (working on Mac OS X)?