A centrifuge comprising a rotor having a rotational axis, at least one receptacle for a blood sample container, controller means for controlling the rotational speed of the rotor, at least one optical transmitter for transmitting an optical signal, at least one optical receiver for registering the amplitude of the optical signal, where the optical signal is configured to pass through the blood sample container where the optical receiver detects the amplitude of the optical signal when it is directed through the blood sample container, where the amplitude of the optical signal reflects the translucency of the blood sample, where the controller means is configured to discontinue the rotational movement of the rotor when the amplitude of the optical signal over time has fulfilled a predefined pattern indicating that at least the fibrin compression phase of the blood sample is started.
