For precision uses, better than an analog one
For recreational orienteering, or survival, all you need is an inexpensive analog compass. For sea navigation, and for trail making, surveying, wildlife monitoring, or anything else where consistently exactitude is require, this scope is probably what you want. Waterproofed, and illuminated at night with fiber optics, these compasses can supplement GPS finders.
Traditional compass designs for hikers are unreliable and hard to use. A magnetized needle wobbles on a primitive bearing, and its accuracy is affected by local mineral deposits. Enhancements of this basic design are still unsatisfactory; for instance, you may find yourself peering into a hinged mirror, trying to focus simultaneously on the wobbling needle in front of you, and a distant object reflected in the mirror, upside-down.
After much searching I found that marine supply companies seem to make the most advanced compasses. I bought a KVH Datascope for about $300. It is designed as a monocular; you look through the unit, which provides 5x magnification, crosshairs, and a digital readout superimposed, accurate to +/- half a degree. This is a sighting compass, meaning that you sight a distant object in the direction in which you wish to travel, walk toward that object, taking another sighting, and so on. The fact that the compass is still accurate if you don’t hold it level (it has a 20 degree tolerance) is a big plus; traditional compasses are useless unless you manage to hold them almost precisely level.
Calibration of the compass is very simple, after which you dial in the deviation of magnetic north from true north in your area. (This information is available on any topo map.) Supposedly the compass is smart enough to compensate for local deposits of ferrous metal, power lines, etc. All I know is that I was finally able to locate the small metal pegs marking the corners of my 40 acres in the middle of nowhere. A professional surveyor’s compass had not enabled me to do this.
The Datascope requires three button-type batteries, and must be recalibrated each time you change the batteries, because each new set of batteries has slightly different magnetic characteristics. My first set has lasted two years so far. The compass comes in a nice padded carrying case, includes a digital clock, is supposedly “totally waterproof,” and weighs 11 ounces. If you’re tempted to buy one, check Google; I found online prices varying by as much as $150.
— Charles Platt08/27/06
(Since this review posted, it's been brought to our attention that screen failure is a relatively common issue, and the product warranty only lasts one year. Additionally, CT readers and other reviewers online have cited spotty customer service. If you can recommend another Digital Compass, please let us know. -- SL — editors)