Bed levelling procedure for Prusa Core One

This is missing part of Prusa documentation about improving bed levelling on Prusa Core One. It's not necessary at all because of perfect first layer feature, but you can improve your feelings about print results if bed level deviation is as low as possible.

Follow these steps to improve bed levelling on your Prusa Core One:

1. Print Bed level meter using 0.10 mm layer height on your printer as is. The precision is good enough now. It contains 20 blocks of size 5x5 mm with height from 1 mm to 3 mm with 0.1 mm step.
   You can customise the meter on onshape
2. Mark tallest block (3 mm), lowest block (1 mm) and every 5 blocks in between (2.5 mm, 2.0 mm middle block and 1.5 mm) for better recognition during measuring
3. Prepare 3x M3 bolt (approx. 15-30 mm long) and nut. Screw nuts on bolts.
   
4. Screw bolts (with nuts on it) into Core one holes on bottom plate inside the printer. Screw it fully but loose
   
5. Run Z-axis calibration.
   
6. Set bed to position 275 mm. (after calibration the bed position is 274 mm).
7. Screw bolt anti clockwise to touch the bed from the bottom.
   
8. Run Z-axis calibration again.
9. Set bed and head position to these three positions and measure the height between bed and nozzle for each.
   1. x = 20,   y = 5,      z = 0
   2. x = 235, y = 5,      z = 0
   3. x = 125,  y = 220, z = 0
      
      
10. Adjust bolts by following rules:
    1. For the first run you can only shrink the gap height, start with bolts corresponding to positions with highest gap height.
    2. To shrink gap height screw bolt anti clockwise, one turn shrinks gap by 0.5 mm
    3. To extend gap height screw bolt clockwise, one turn extends gap by 0.5 mm
11. Repeat from point 8 until gap height between bed and nozzle is equal for every point. (You need to run Z-axis calibration, position, measure height and adjust screws again and again until it's done).
12. Fix bolts in position by holding bolt (to prevent rotation) and turn nut in clockwise direction.