Circle calibration

I made this little thing to check my actual results from printing circles, as I have had some issues with internal diameters being a bit to small. With this as reference, I can easily make up for that when drawing other stuff.

Print, measure actual result with calipers(or ruler). Compare to drawing reference, might be a good idea to download that as well.

BTW; if anyone know of a good setup to print more precise inner diameteres for a Printrbot LC(v2) using Slic3r I'd be happy to get them! The thing is propperly calibrated, all outside dimensions come out right.