E Step Calibration Ruler

120mm ruler with filament grove. Put the side closest to zero flush against a reference point and mark the other end on the filament. Calibrate against a 100mm extrude length of filament and the mark should land on 0mm. Measurements on the ruler from where it should land.

Never calibrate off a single result. Do it twice, better yet three times. Inconsistent results is a good indicator that your extruder has an issue (gummed up with filament dust, loose screw, gummed up filament contact teeth etc). If you do get an issue, start with visual inspection (make sure there are no cracks in the extruder body, is there a dust build up in the drive gears or filament teeth, is Bowden tube loose etc). Give it a good clean and SMALL amount of lube on drive gears for dual extruders - better yet disassemble, clean and re-assemble. If you do disassemble, check for wear on the bores of the drive (an idle if applicable) rollers. If everything fails - throw money at the problem and get a new extruder