or Horizon Mirror half clear glass half mirror, on a sextant it allows the observer to view the horizon at the same time as a reflection of whatever is showing in the Index Mirror. Read more:

a DR position which has been adjusted to allow for Set and Drift.

are the prevailing west-to-east winds of the middle latitudes of both hemispheres on Earth.

the angle between True North and Magnetic North.

">Vector charts; a type of electronic chart.

geographic north as opposed to magnetic north

steady easterly winds that blow through the tropics and subtropics.

two fixed objects in lined up by an observer.

a method of lining up charted objects to obtain an LOP.

the distinctive shape on top of a buoy.