Between 1514, the first printed reference to a cross-staff (also known as a 'Jacob's staff'), and the last known example produced in 1805, many thousands of cross-staffs were manufactured by a wide range of instrument makers principally in Holland and Britain. Despite the instrument's enduring popularity with mariner's over these three centuries, once it was finally made obsolete by the advances in octant and sextant scale division, it rapidly lapsed into obscurity. Once dissembled, the component parts of a cross-staff (i.e. the staff and four crosses), went largely unrecognized and became separated. The example offered here was identified by a chance conversation between the vendor and an instrument enthusiast, brings the total known quantity of genuine cross-staffs to less than one hundred, the majority of which are incomplete.

Erven van Hendrik Mooy was the widow of Hendrik Mooy, continued a business based in Nieuwebrugsteeg (Amsterdam) which specialised in cross-staffs. Hendrik took over the business from his second cousin Isaac Swigters in 1750, on his death in 1765, Erven continued production until 1795. As the example offered in this lot is signed for 'H. Mooy', it is possible that she was either retailing old stock or was continuing to sign the instruments in her late husbands name.