Compass

What Is a Compass?

Parts of a Compass


There are many types of compasses ranging from tiny thumb compasses to complex high-tech gadgets. For most hikers and outdoors guys like us, an orienteering compass works just great and that is what we'll discuss here.

compass parts

Not all compasses include each of these parts and some compasses include even more.
Baseplatehard, flat surface on which the rest of the compass is mounted. It has a rulers on its edges for measuring distances on maps. It's edge is straight and useful for laying lines on a map
Scaleseach edge of a compass may have different rulers for use with different map scales
Direction-of-Travel Arrowmarked on the base plate. You point this the way you will be traveling
Magnifierfor seeing small map features better
Index Pointerbutt end of the direction-of-travel arrow. It ends right at the edge of the dial and is where you take degree readings
Dialring around the housing that has degree markings engraved. You hold the dial and rotate it to rotate the entire housing
Declination Marksuse to orient the compass in an area with known declination
Orienting Arrowmarked on the floor of the housing. It rotates with the housing when the dial is turned. You use it to orient a compass to a map
Orienting Linesseries of parallel lines marked on the floor of the housing and on the base plate
Needlemagnetized piece of metal that has one end painted red to indicate North. It sits on a fine point that is nearly frictionless so it rotates freely when the compass is held fairly level and steady
Housingmain part of the compass. It is a round plastic container filled with liquid and has the compass needle inside
Bubblea bubble of air in the housing liquid is useful for making sure you are holding the compass fairly level
Mirrorlets you see the compass face and distant objects at the same time. Useful for emergency signaling
Sightimproves aiming your compass at distant objects

How a Compass Works


There is a huge magnetic field around the earth. It is huge, but it is not very strong. The magnetized needle in a compass is aligned with this magnetic field. As the image below shows, the composition of the earth acts as a huge bar magnet sitting upside down in the middle of the planet. Since its South end is at the north pole and its North end is at the south pole, the North end of a compass needle is pulled north.

compass earth magnetic field

Your compass has to have a very light needle sitting on a pivot that has almost no friction. This is because the earth's magnetic field is weak and would not be able to turn the needle. You can even make your own compass just for fun.

Next: Reading a Compass

parts of compasses The Tate's Compass company manufactured over 1 million compasses a year.
But, one day the red and white paint got mixed up so all their compasses pointed the wrong way.
The company went out of business and the well-known saying was created:
"He who has a Tate's is lost!"


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