How to Use a Navigational Quadrant

Navigating across the open ocean is no easy task and for the first explorers, wandering even slightly off-course could prove fatal. As a result, accurate navigation was essential, and the navigator's quadrant was one of the primary tools in that arsenal. This fundamentally simple device could help captains and crew determine their latitude, as long as there is clear sky.

Instructions

1. Steady your quadrant in a stable position, so that your plumb-bomb hangs straight down. While at sea, early mariners used to do this by hanging the quadrant in the rigging of the ship.

2. Sight along the quadrant's straight edge with the curved edge facing down, such that you are looking directly at either the noontime sun during the day, or Polaris the North Star at night. Both require clear conditions, and staring at the sun obviously entails risk of personal injury.

3. Mark the angle where the plumb-bob string rests. This angle will correspond to your latitude - if the North Star is 48° above the Northern horizon, than you yourself are at 48° North.

4. Adjust your navigation accordingly. When sailing through vast bodies of open water, early mariners used to practice "latitude sailing", by which they'd simply maintain the same latitude the whole way across the ocean.

Tips & Warnings

• Quadrants were later developed so that navigators didn't need to stare into the sun to calculate their position. The Davis quadrant, for example, can be used with your back to the sun.