I suspect there's no unified model that is ideal, yes. But I'm not a designer or ui expert at all, just have built some interfaces using it. CSS's approach seem

I suspect there's no unified model that is ideal, yes. But I'm not a designer or ui expert at all, just have built some interfaces using it. CSS's approach seems more practical, basically letting you define a set of constraints for different scenarios with overrides and defaults available. Again and I really want to stress this because it's important and maybe unintuitive or hard for us to accept as engineering minded folks. You can't sit down with a pen and paper and numbers that describe a good interface in a given scenario (size, ratio, pixel density, colorspace, etc), and using only math transpose that interface to a different scenario. If you can do this, it's because you have enough experience and intuition with the measures to make good estimates. But these are not properties of the numbers. The numbers describe a good interface, they don't create it.