G21        ;metric values
G90        ;absolute positioning

G28 X0 Y0  ;move X/Y to min endstops
G28 Z0     ;move Z to min endstops

; if your prints start too high, try changing the Z0.0 below
; to Z1.0 - the number after the Z is the actual, physical
; height of the nozzle in mm. This can take some messing around
; with to get just right...
G92 X0 Y0 Z0 E0 ;reset software position to front/left/z=0.0
G1 Z15.0 F400  ;move the platform down 15mm
G92 E0         ;zero the extruded length

G1 F75 E5      ;extrude 5mm of feed stock
G1 F75 E3.5    ;reverse feed stock by 1.5mm
G92 E0         ;zero the extruded length again

G1 X100 Y100 F3500 ;go to the middle of the platform
G1 Z0.0 F400   ;back to Z=0 and start the print!