The standard bed level correction procedure can be very time consuming and tedious. This calibration sheet is designed to be used in combination with a conventional flatbed document scanner. The line widths are analyzed on the scanned image using edge detection and measurement tools in Inkscape. That way precise adjustments can be performed and optimal calibration achieved. The print time is also reduced to 8 min instead of 30 min for the standard calibration file. These improvements speed up the calibration process and make it a lot easier.

Procedure:

1. Preheat the printer for best results.
2. Print the scanner-bed-level-calibration-spiral.3mf file in a white filament to achieve a good contrast to the steel sheet print bed.
3. Place the  steel sheet with the print still attached on a flatbed scanner
4. Scan using a high resolution (600dpi) and save as a JPEG file.
5. Import the JPEG into Inkscape.
6. Click on Path>Trace Bitmap.
7. Check Invert image and then click Apply to perform the edge detection.
8. Use the measurement tool to perform multiple measurements on lines in front, back, left and right.
9. Calculate a mean value for each direction. The ideal value should be 0.5 mm
10. Adjust the printers level correction parameters for each direction according to the following rule:
    mean_value/0.5*200-200
11. Repeat at step 1 until you are happy with the result.
    
     

I was able to perform calibration within three cycles, while it took me hours with the standard procedure. Good luck and happy printing :)