To make calibration easy, use this large easy to print piece. 110mm for x and y, 4mm height. All squares are 10mm x 10mm.
The difference to smaller calibration pieces is that you can find really tiny errors with this. I found a 2% error in my print, 3 mm at this size. A standard 20mm calibration cube would have given you a .4mm difference. Still measurable but a lot more difficult.
Print, cool, measure, calibrate, print again, measure, calibrate again :)
Calibration is done like this
Get your X or Y calibration value from Slicer.
Measure the X or Y length of the piece
Use following formula
(110 x OldCalib) / Measurement = NewCalib
So my old value was 61.2555 for X and I measured 107.50mm.
110 x 61.2555 = 6738.105
6738.105 / 107.5 = 62.6800
So i now have a better calibrated bot!