Calibration square for x/y and skew correction

Square for calibration X-Y inner and outer size compensation. 
Also aplicable for checking skew value by measuring diagonals.

Outer size is 90mm, inner size is 70mm. 
After measuring size difference should be set into X-Y hole/contour compensation parameters in slicer app.

Also it can be used for calibration stepper motor rotation distance.

Design by Tarasyk on MakerWorld (license: BY).