When printing models with an opening in the interior (circles or rectangles/squares) the outer dimensions seem to measure out ok, within .1mm of what it should (usually its slightly over what it should be, but close)

The interiors however are about .5mm narrower than they should be. I'm not sure what. Anybody have any clue what I should change?

I've read this is a common problem with Sli3er on circles, but haven't read that its an issue on other opening shapes (like squares)