A method for determining a reference position for a pipetting needle which is part of an automatic analytical apparatus. The method comprises the following steps: (i) a first measuring step for measuring a first displacement error (Delta X) in a displacement of the pipetting needle (72) effected by a transport device, (ii) a first correcting step for correcting the first displacement error by means of a corresponding correction of an angular error (Phi) of the initial angular position of the pipetting needle, (iii) a second measuring step for measuring a second displacement error (Delta Y) in a displacement of the pipetting needle in a second direction (Y-axis) perpendicular to the vertical plane, (iv) a second correcting step for correcting the second displacement error (Delta Y) by means of a corresponding change (+-) of the angular position of the pipetting needle along a circular path, (v) a third measuring step for determining the position of a vertical reference line, and (vi) a fourth measuring step for determining the position of a reference point ((X 0 , Y 0 , Z 0 ) along said reference line. |