The mathematical algorithms used in our fundamental parameter Rietveld program BGMN are capable for describing learnt profile peak shapes, too. We describe this method using a D 5000 goniometer plus Goebel mirror as an exemplary geometric set-up. In detail, the three steps 1. determination of size/strain parameters of standard specimen Y2O3 Using raytraced profiles on a conventional XRD 3000 TT diffractometer 2. learning Y2O3 profiles on the D 5000 diffractometer 3. measurement of the unknown CeO2 sample on the D 5000 diffractometer are explained. This method is recommended as an alternative for solving the problems in description of parallel beam optics or OED.