An ultrasonic measuring unit and a method for detecting ultrasonic signal run-times, in which the ultrasonic measuring unit has two ultrasonic transducers for coupling ultrasonic signals into a flowing medium. Analysis electronics are provided to be accommodated on or in a flow tube, in which a gaseous medium such as circulating air flows. A probe unit is accommodated in the flow tube, the probe unit being assigned a temperature probe having a flow around it, whose measured value is used for correcting a temperature signal detected by ultrasound.