Is there a way to have an equation mix units.

For example, my model units are in inches. But I want an equation to be something like "D1@Sketch1" = "D2@Sketch1" + .003mm.

I tried the exact example above. But SW wasn't very happy about it. I know this sort of thing can be done within a dimension modify box.

I realize that it would be just as simple to convert the .003mm to inch units. But, there is a reason why I would prefer it to show up as metric units in the equation. Any other ideas?