Method for position determination of a robot arm in an automatic liquid handling system comprising a substantially horizontally aligned worksurface for the placement of containers or container carriers and at least one robot arm having a drive, for example, a pipetting robot having at least one pipette for aspirating and/or dispensing liquid samples or a logistics robot having at least one gripper finger for moving the containers or container carriers, and a control unit which is operationally connected to the robot arm, wherein a measuring probe having a first electrode is arranged on the robot arm, which, together with a second electrode, which is formed by at least a part of the worksurface or at least a part of the container or container carrier forms a measuring capacitor, which is operationally connected to a measuring unit for measuring an impedance, in particular a capacitance, of the measuring capacitor, wherein the worksurface or the container or container carrier has at least a first and a second recess (21, 21') or depression, which cause changes (ΔC 1, ΔC 2) of the impedance, in particular the capacitance, of the measuring capacitor, characterized in that the first and second recess (21, 21') or depression is triangular or trapezoidal, and wherein the worksurface or the container or container carrier has two identical triangular or trapezoidal recesses (21, 21') or depressions, which are arranged in particular pivoted by 180° in relation to one another, wherein the method has the following steps: a) moving the measuring probe along a first path (p 1), in particular a substantially horizontal path over the worksurface or the container or container carrier, wherein the first path (p 1) traverses the first and second recesses (21, 21') or depressions; b1) detecting a first change (ΔC 1) of the impedance, in particular of the capacitance, of the measuring capacitor at a first point (x 1) of the first recess (21, 21') or depression along the first path (p 1); b2) detecting a second change (ΔC 2) of the impedance, in particular of the capacitance, of the measuring capacitor at a second point (x 2) of the first recess (21, 21') or depression along the first path (p 1); b3) detecting a third change of the impedance, in particular of the capacitance, of the measuring capacitor at a first point (x 1) of the second recess (21', 21) or depression along the first path (p 1); b4) detecting a fourth change of the impedance, in particular of the capacitance, of the measuring capacitor at a second point (x 2) of the second recess (21', 21) or depression along the first path (p 1); c) establishing at least one first reference space coordinate (x Ref), for example, an x or y coordinate, for the control unit based on the first and second point (x 1, x 2) of the first recess (21, 21') or depression and the first and second point (x 1, x 2) of the second recess (21', 21) or depression along the first path (p 1). a) moving the measuring probe along a first path (p 1), in particular a substantially horizontal path over the worksurface or the container or container carrier, wherein the first path (p 1) traverses the first and second recesses (21, 21') or depressions; b1) detecting a first change (ΔC 1) of the impedance, in particular of the capacitance, of the measuring capacitor at a first point (x 1) of the first recess (21, 21') or depression along the first path (p 1); b2) detecting a second change (ΔC 2) of the impedance, in particular of the capacitance, of the measuring capacitor at a second point (x 2) of the first recess (21, 21') or depression along the first path (p 1); b3) detecting a third change of the impedance, in particular of the capacitance, of the measuring capacitor at a first point (x 1) of the second recess (21', 21) or depression along the first path (p 1); b4) detecting a fourth change of the impedance, in particular of the capacitance, of the measuring capacitor at a second point (x 2) of the second recess (21', 21) or depression along the first path (p 1); c) establishing at least one first reference space coordinate (x Ref), for example, an x or y coordinate, for the control unit based on the first and second point (x 1, x 2) of the first recess (21, 21') or depression and the first and second point (x 1, x 2) of the second recess (21', 21) or depression along the first path (p 1).