There are a number of important points to keep in mind when buying a compass. While it may be suitable, for recreational use, to find the cheapest compass one can buy, these are not acceptable for those who are depending on a compass for survival or for regular use. Also, the type of compass one uses may depend on what types of application it is being used in.
Many prefer to use a compass when hiking, especially if their adventures will take them away from the marked trails. In these applications, just any compass will not do. It is important to find one with a rectangular face plate and a declination adjustment.
The declination is one of the most important parts of the compass. While many believe that a compass points to the north pole, this is only partially true. It points to the magnetic north pole, which constantly moves and is not truly directly north for most of the world. Therefore, an adjustment is needed to make the compass totally accurate. Without a declination adjustment, the compass could be off as much as 30 degrees. Some compasses will have instructions for your location, but the U.S. government also has a Web site that can be used to find your declination adjustment.
The rectangular face plate is also important. It should be transparent so it can be overlayed on top of maps to provide a good understanding of where you are going and what may be along the way. This will provide good visual clues to help you keep on track.
Of course, for those who are not outdoors people, but simply like to keep track of their direction of travel while in a vehicle, there are also many different compasses to choose from. They normally sit on dash boards or stick to the windshield. These are not compasses in the truest sense of the word but do indicate direction of travel with some degree of certainty. Again, because these cannot be adjusted for declination, they are generally off to a certain degree.
For those who want a truly foolproof compass, most handheld GPS units offer a compass feature. This may be the most accurate "compass," especially if you have a waypoint you are trying to get to. The compass feature will always give you the general direction you need to go in order to reach your desired destination, once that destination is inputted into the unit. The unit will also indicate your general direction of travel.