Description
The backstaff is a navigational instrument used to find latitude. It was introduced during the 17th century as a replacement for the crosstaff. With a crosstaff the Ship’s navigator would have to look directly into the sun which was often to bright. To use the backstaff the navigator was able to stand with their back to the sun and use the shadows cast on the instrument to take readings.

To use the backstaff the backsight and the horizon slit are lined up. The shadow vane on the small arc is moved until its shadow falls onto the horizon slit. The combined angle of the backsight and the shadow vane gives the angle of the sun and therefore the latitude.

The backstaff has a standard pattern of 2 main “limbs”, in ebony rosewood, pear wood or mahogany with the arcs and occasionally the braces in boxwood.

The backstaff was replaced by the octant which began to be made commercially from the mid 18th Century. Unlike the backstaff the octant was not affected by the movement of the ship when the navigator attempted to take readings.

Both the octant and backstaff continued to be produced and used into the 19th Century despite competition from the more accurate and versatile sextant. This may be because these instruments were cheaper and more affordable than the sextant.