At the laboratory for INAA in Delft, the final approval of the analysis' report partly depends on the quality of the results of simultaneously processed reference materials (RM's). An extensive databank exists holding the information on RM type and analysis conditions. This information can be convented into control charts. The control charts can display (1) an element concentration in one RM as a function of moment of analysis, (2) an element concentrations in one RM as a function of the concentration of an interfering element, (3) an element concentration in all RM's, and (4) the nomalized concentrations of all elements in one RM. The inspection of the various chats facilitates the decision on, e.g., the need for renewed standardization, the fitness-for-use of a RM, any analyst-dependent results, rigidity of the spectrum analysis software etc.