Draw bar with an evaluation device

The coupling (10) has a dome carrier (14) comprising a clutch arm. A dome element (23) i.e. clutch ball (22), is arranged at free end of the dome carrier for attaching a trailer (92). A support (11) is firmly or movably arranged at a towing vehicle (90). A force sensor (30) detects force acting on the dome element by the trailer and outputs a force signal representing the force. An evaluating device (50) determines value of load and/or mass value of the trailer based on the force signal and angle value. The evaluating device comprises acceleration and/or temperature sensors. An independent claim is also included for a method for determining mass value of a trailer# an evaluation module.