Take a business card and move the print head down to where you can just feel the card being held in place by the friction of the nozzle resting on it. then select prepare in the lcd menu then select set home posistions. everything g should read 0.00 across all axis at this point. in your slicer settings make sure you remove any g28 or g29 commands. if you notice any dragging across your bed at this point when starting a print then your bed is not level.
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