Abstract: A mixer in particular for viscous elastic materials has a processing channel having an outlet opening at one end which can be closed. The materials can be transported and simultaneously mixed along the processing channel using a a transport device. A feedback channel branches off from the processing channel near the outlet end and feeds back into the processing channel at an upstream location so that the material mixture can be circulated though the processing channel and the feedback channel when the outlet opening is closed. In order to be able to measure rheological quantities of the mixture during the mixing procedure, the feedback channel is configured as a measurement path. Towards this end a pressure sensor device can be provided for in the feedback channel to measure the transport pressure in the transported material mixture at at least two mutually separated cross sectional locations of the feedback channel.