The electrical machine includes a movable part and a static part. The movable part rotates in relation to the static part around a dedicated rotary axis. An air-gap is located between the rotating and the static part of the machine. A device is positioned and used to measure the spacing of the air-gap. The static part and/or the movable part is coupled with an actuating-unit, which changes the relative position of the static part in relation to the movable part to adjust the spacing of the air-gap.