Calibration of a thread tensioning force meter on a texturing unit for a false twist machine was previously performed differently depending upon the direction of withdrawal, that is forwardly or rearwardly, of the thread from the texturing unit. The thread passes the tensioning force meter by passing over a spring biased support abutment connected with a meter. In the invention, the outlet past the tensioning force meter includes a withdrawal point and slightly upstream of that point a calibration point, which points are separated by a thread eye through which the thread passes. The location of the calibration point is selected with respect to the withdrawal point and with respect to the position of the abutment engaged by the thread that regardless of whether the thread is withdrawn forwardly or rearwardly of the meter, the thread continuously contacts the calibration point. In one direction of withdrawal, the thread only contacts the calibration point. In the opposite direction of withdrawal, the thread first contacts the calibration point and then contacts the thread guide outlet, which holds a thread passing through the thread eye against the calibration point.