A compass is an instrument that helps people navigate by using the natural magnetic field of the Earth. It consists of a magnetized pointer or needle set in a face similar to a clock. Instead of numbers, the face is marked with the directions North, South, East, and West. Some compasses have additional markings that show the secondary directions such as southwest, northeast, and the like.
A lensatic compass is one of the many kinds of compasses. It has a magnetized dial instead of a plain needle. The dial is the one marked with the directions while the face is marked with numbers used for determining more precise directions. It has a lensatic card attached to it. This allows users to read the compass without needing to glance down and look at the compass’ face directly. A protractor is necessary for it to be used with a map.
The circumference of the compass face is divided into 6400 units. One unit is actually 1 meter of separation at a distance of 1,000 meters. One mil is also 1 yard at 1000 yards. This is the military (or mil) system.
Taking a Bearing
Unfold the top cover such that it stands in a 90° angle with the compass card. Have the lens erected to approximately a 45° angle. See to it that the thumb hook is directed downwards.
Put your thumb into the hook of the compass to keep it steady. While facing the target object, set the sighting wire to its center.
Read the fine degree markings of the compass card without taking your attention away from the object. Do this by moving the lens up and down. Read the bearing in military system or in degrees.
Setting a Bearing
Face your target object and take the bearing in degrees. Turn the moving marking and align this with the magnetic north shown by the compass card.
Determining the directions through the magnetic north and the marking will allow you to familiarize yourself with the spatial orientation of the place you are traveling.
Following a Bearing
After familiarizing yourself with the directions, choose a landmark in the distance and use it as a point of reference while traveling. When the reference point becomes invisible due to hindrances like clouds, trees, etc., just follow the bearing shown on the compass. Occasionally verify your location and direction by taking a new bearing to the landmark.
Orienteering with the Lensatic
Most up-to-date lensatic compasses have a square case that can be used to triangulate your reference point to your position. One side of the case always has measurements that can be used as a ruler for military grid maps.