Ultimate Calibration Cube

10 in ONE

• Dimension of planar sides = 20mm
• Dimension diagonally = 25mm over chamfer (also over round edges) - parallelism & orthogonality (skew)
• Inner Dimension, window is 10mm and 12mm diagonally (4mm walls)
• Bottom has Two rings .2 and .35 mm wide for several layer heights (1st layer squish)
• Bridge 2×10×2mm 
• Overhangs 45° and ~35° edge (~55° overhang) on the inside - up to 90° in the windows
• 90° corner for alignment of sides with bottom and top skin and extrusion / acceleration 
• Ringing and detail check on the letters
• Stringing check when printing the corner column (travel through windows)
• Bottom check via unsupported roof in  the center and Top/Ironing

Orthogonal?

Why is it so hard to detect a skewed gantry with a normal calibration cube?

A ruler will only see the 20mm, and the caliper will measure the parallel sides and only notice .05 less which is within printing tolerances. But when measure diagonal you notice a much bigger difference of 2mm (± 1mm)  in this exaggerated example with 4° deviation. 

This is why the Ultimate Cube uses chamfers on the Z corners (can't print clean round in that direction) and round on the XY plane. A perfect Ultimate cube will measure 25mm diagonally.

a normal cube can be measured diagonal ↦ 28,2842712… mm  but it depends on the 90° edge condition and printing as there is no flat/round surface.

SpeedCube

Also a speed test with walls, retractions, travel, infill, bridging, details 

better measurement

Measure XY, XZ and YZ diagonally and all are correct (25mm) - all 3 axis are dimensionally correct and parallel and orthogonal.