This is the calibration prints that I always use when I deicde to try out the new version of skeinforge. I can't find how to make a derivative, so these will be derivative as soon as someone shows me the obvious bright red button I missed.
The thin walled box is Dmatsumoto's thingiverse.com/thing:1637. it is unaltered, because it's just perfect.
The two other blocks are alterations of Bre Pettis's 40mm cube thingiverse.com/thing:477.
I learned this technique from several places, but I didn't understand it till I read Makerblock's wonderful blog post at makerblock.com/2010/02/makerbot-skeinforge-tuning-and-calibration/, check it out, he makes since (unlike me).
I can usually dial my skeinforge in almost perfectly just using these 3 items.