The VOS ordered in 1739 15 cross Staff‘s ‘met dubbele platen voor 5fl’ at the Van Keulen firm.
From 1741 onwards they started to order octants, but at that time the Backstaff was already in use but competing with the Dutch method of the Cross-Staff.
In 2004 Mörzen Bruyns completed the known list of 129 (94 + 34) cross-staffs. He inspected the pictures of our cross staff. ( 9/11/2020).
The van Keulen family operated a chart-making and publishing firm in Amsterdam for nearly 200 years. It was founded by Johannes van Keulen in 1681 who registered his business as a “bookseller and cross-staff maker. Gerard van Keulen, son of Johannes, born 1678, took over the business in 1714 and continued to expand the firm.
In 1726, Johannes van Keulen (II), son of Gerard, took over the business. In 1743, Johannes was appointed "Official Chartmaker of the Dutch East Indies Company. Although the firm had been supplying charts to the East Indies Company for many years prior.