This analysis emphasizing co-occurrence and systematic attention to archaeological context allowed Thomsen to build a chronological framework of the materials in the collection and to classify new finds in relation to the established chronology, even without much knowledge of their provenience. In this way, Thomsen's system was a true chronological system rather than an evolutionary or technological system. Exactly when his chronology was reasonably well established is not clear, but by 1825 visitors to the museum were being instructed in his methods. In that year also he wrote to J.G.G. Büsching: