A computer program for simulating output control has been developed. The calculations in the program follow the standard EN 14081-3:2005, where output control is described. The purpose of the simulator is to make it possible to improve the yield without jeopardizing the safety of the produced boards by testing different approaches in grading. The program is a research tool, as well as a program to use in production where output control is used. In the program is it possible to test e.g. the influence of change of IP-values, number of grades, pre-grading of logs, raw material region, etc. The result of a simulation is shown both as diagrams and numeral. The standard C-grades are pre-programmed with K-, Y- and Z-coefficients according to the standard. Other grades can be added by the user.