Calibrating wall thickness

When printing the single wall test piece, I've read to shoot for a value of about .7mm for PLA, but I'm not sure why? I'm having issues where an objects outer diameter comes out spot on, but the inner diameter is much too small. This was most noticeable with a small hollow cylinder designed to fit around an LED. Perhaps its a skeinforge 40 setting I mucked up but I can't help to think that it's related to wall thickness..

Circles come out smaller because a circle is printed as a polygon inscribed inside the circle among other things. Please read nophead's blog: [hydraraptor.blogspot.com].

As far as the wall thickness of a single-walled piece, it depends on your layer thickness and the width to thickness ratio. There's nothing particular about 0.7 mm. For example, if you're layer thickness is 0.3 and your width over thickness ratio is 1.5, then the wall should be 0.45.

I've been using the polyholes module, it works great Haven't tried to print another cylinder, but I have my walls looking great at .22 layer thickness.