The present invention relates to a method and assembly for opening the nips (9,10) of a calendar comprising at least two elements (1, 2; 3, 4) brought to a nip contact with each other, especially for performing the nip opening at a break or damage occurring in the web (5) being calendered. The tension of the web (5) being calendered is measured at multiple points over the cross-machine width of the web (5) and the calender nips (9,10) are opened when the measured web tension at a preset number of points over the cross-machine width of the web (5) has fallen to a limit value that by a decision-making algorithm monitoring the tension profile of the web (5) is interpreted to indicate a web break situation or other damage on the web (5) requiring opening the nips (9,10).