A long thin wooden rod attached to the display with a rope. There is a piece of wood on the rod you can move back and forth. The display reads 'try navigating with the cross-staff.'

The Europeans Arrive - the Portuguese and the Dutch

Finding your way in an unknown world - the cross staff

The cross staff, also known as the ‘Jacob’s staff’, is believed to have been developed around 1340 by the French mathematician Levi Ben Gerson as a navigational tool to measure the altitude of a celestial object above the horizon. With the angle so calculated, a navigator could determine the latitude on the surface of the Earth of their ship. It was used from around the mid-14th century until as late as the mid-17th century. While the cross-staff was an improvement on earlier navigational tools, such as the Arab ‘kamal’, it came with some of its own issues. Firstly, the user was required to look at two points at once, which meant accuracy for large angles was not quite practicable. Secondly, because the user was required to use a celestial body to determine the angle, it meant looking directly into the sun during the day, which could potentially result in blindness. That is one reason why sea captains in the old days wore eyepatches. It is worth noting here that, contrary to popular misconception, many people of the past did not believe the Earth was flat; even the ancient Greeks conceptualised the Earth as being a globe supported on the back of Atlas. It is simply not practicable to navigate a vessel around the globe if you think that you are on a flat surface.

Line drawings of navigational instruments on yellowed paper.

An astrolabe, a cross-staff, and a back-staff or Davis's sextant.
Credit: drawing after Edmund Gunter, 1624

A drawing of a man holding a cross-staff up to his eye. He lines the top of the cross-bar up with the sun and the bottom with the horizon.

Usage of a cross staff for navigation.
Credit: Omurtay, licensed under CC BY-SA 4.0

The Museum's replica cross staff.
Credit: WA Museum