A method and an arrangement (1) for determining an actual value of the gap (4) between the work piece (2) and the electrode (3) during a process of electrochemical machining. According to the invention first process control means (30) are arranged to supply a set of machining current pulses (Im) to the electrode and the work piece. Second process control means (32) are arranged to perform a measurement of an operational parameter (U) representing a value of the gap (4) in real time under operational conditions. The second process control means (32) comprise means to determine the actual value of the gap (55a) based on the measurement of the operational parameter and logical unit (55b) to actuate the positioning means (8) to translate the electrode (3) in case the measured value of the gap deviates from the preset value of the gap.