A method for calibrating the position of slitter blades (23, 24) of a slitter-winder in a fiber web production line, where movement of the fiber web through the slitter-winder defines a machine direction, and a cross machine direction is defined perpendicular to the machine direction, wherein the slitter-winder has a plurality of cross machine direction arrayed slitter blade pairs (23, 24), and at least one slitter blade (23; 24) of each slitter blade pair (23, 24) is mounted to a carriage (21; 22) for movement upwards and downwards with respect to the carriage (21; 22) for changing a distance with respect to a second slitter blade (24; 23) of the slitter blade pair (23, 24) for engaging and correspondingly opening each slitter blade pair (23, 24), and wherein the carriage (21; 22) is mounted for movement in a cross machine direction on a guide (11; 12) of the slitter-winder to slitting positions for slitting the fiber web into partial webs in the machine direction of the fiber web, the method being characterized by the steps of: measuring in each pair of slitter blades (23, 24) with a laser having a cross machine direction extending beam, a cross machine direction position of a first slitter blade engaged with a second slitter blade forming each pair of the plurality of slitter blade pairs (23, 24), wherein the first slitter blade is mounted to a first carriage movable in the cross machine direction on a first guide in the slitter-winder, and wherein the second slitter blade is mounted to a second carriage movable in the cross machine direction on a second guide in the slitter-winder, wherein the measuring in each pair of slitter blades (23, 24) is conducted while the slitter-winder is in standstill and no fiber web is running, and wherein slitter blade pairs (23, 24) between the laser and the pair of slitter blades (23, 24) being measured are open so as not to block the laser beam from reaching the pair of slitter blades (23, 24) being measured; measuring a position of each first carriage in the cross machine direction with a first carriage position sensor; comparing the cross machine direction position of each first slitter blade, with the position of each first carriage in the cross machine direction as measured with the first carriage position sensor; and calibrating each first carriage position sensor, so that each first slitter blade can be positioned based on each first carriage position sensor. measuring in each pair of slitter blades (23, 24) with a laser having a cross machine direction extending beam, a cross machine direction position of a first slitter blade engaged with a second slitter blade forming each pair of the plurality of slitter blade pairs (23, 24), wherein the first slitter blade is mounted to a first carriage movable in the cross machine direction on a first guide in the slitter-winder, and wherein the second slitter blade is mounted to a second carriage movable in the cross machine direction on a second guide in the slitter-winder, wherein the measuring in each pair of slitter blades (23, 24) is conducted while the slitter-winder is in standstill and no fiber web is running, and wherein slitter blade pairs (23, 24) between the laser and the pair of slitter blades (23, 24) being measured are open so as not to block the laser beam from reaching the pair of slitter blades (23, 24) being measured; measuring a position of each first carriage in the cross machine direction with a first carriage position sensor; comparing the cross machine direction position of each first slitter blade, with the position of each first carriage in the cross machine direction as measured with the first carriage position sensor; and calibrating each first carriage position sensor, so that each first slitter blade can be positioned based on each first carriage position sensor.