Calibration block - thin walls, overhang, bridge, holes

This is a calibration thing, that i design to test my printer.
It has several features:
- thin walls in x and y direction 4mm 2mm 1mm 0.5mm 0.25mm
- Holes in different sizes r= 4mm 2mm 1mm 0.5mm
- Overhang test with differnt slopes
- Bridge test with different lengths
the whole block is 50x50x10mm
I did not test it with skeinforge but on repsnapper it works fine.