first edition of a very rare navigation book for the VOC. Only three other copies known. Historical research shows that the intensive collaboration between De Decker and Vlacq led to the production of the first complete logarithm table, which appeared in two different books in a short period of time. One can justifiably blame Vlacq for concealing De Decker's undoubtedly considerable contribution. The best way to do justice to history is probably to consider both De Decker and Vlacq together as the first producers of a complete logarithm table.