Method for calculating and optimizing the diameter of a paper or board web reel based on customer splice location restrictions

A web is wound in a paper or board machine into machine reels, which are run on a slitter-winder to form customer rolls, whose desired diameter and width are determined according to customer need. A continuous-trimming running mode is used in which a desired amount of web is run into a machine reel and, when needed, splicing is performed on the slitter-winder to produce customer rolls with a desired diameter size. The machine reel diameter is determined based on restrictions set on the location of a splice in the customer roll and the amount of broke produced from the machine reel is optimized. Information about the customer rolls to be slit is obtained from a production control system for calculating/optimizing a machine reel diameter instruction for optimizing the diameter of the next machine reel, and the calculated/optimized machine reel diameter instruction is set in the control system of a reel-up.