Compass Types and Selection: Choosing the Right Compass

Baseplate (Orienteering) Compass

The baseplate compass is the standard for map-and-compass navigation. It's a rectangular transparent plastic base with a rotating azimuth ring (bezel) mounted over a magnetic needle housing.

Key components:

• Transparent base: Lay the compass directly on the map for map work. The base contains direction-of-travel arrow and meridian lines.
• Rotating bezel: Graduated in degrees (0-360). Rotate to set bearings. Index line marks where to read the bearing.
• Needle housing: Contains the balanced magnetic needle floating in dampening liquid.
• Needle: Red end points to magnetic north. White or black end points south.
• Orienting arrow: Fixed arrow inside the needle housing. When you rotate the bezel to align with north, you align this arrow with the needle.
• Meridian lines: Parallel lines on the bottom of the housing that align with map grid lines.

Best for: Map work, trip planning, travel in terrain with clear landmarks, casual outdoor navigation.

Limitations: Precision bearing shots are harder than with a lensatic. The needle can be difficult to read in low light.

Top models: Suunto A-10 ($35-45), Silva Ranger ($50-70), Suunto A-30 ($50-65).

Lensatic Compass

The lensatic compass is the US military standard (M1950 and variants). It folds into a protective case and uses a sighting system for precise bearing measurement.

Key components:

• Hinged cover: Folds up to reveal the compass face. Contains a sighting wire for precise line-of-sight bearing measurement.
• Lens eyepiece: Magnifying lens and rear sighting notch. Look through the notch at the sighting wire while reading the bearing in the lens.
• Compass dial: Rotates freely inside the housing (not a rotating bezel — the dial moves with the compass while the housing stays oriented to the user).
• Luminous markings: Tritium or luminescent marks for night navigation.

How it works differently: To take a bearing with a lensatic, hold it level with the case open, thumb through the loop, look through the rear sight notch at the sighting wire, align the wire on the target, and read the bearing shown under the index line through the lens.

Best for: Precise bearing shots at distant objects, military-style navigation, night navigation, conditions where you need to shoot exact bearings to navigate through complex terrain.

Limitations: More complex to use than a baseplate. Not designed for map work — you need to hold it differently and the transparent base is absent. Heavy and bulky compared to baseplate.

Models: Cammenga 27 ($50-70, tritium illumination), Cammenga 3H ($70-100), Stocker & Yale ($60-80).

Thumb Compass

A small compass designed to strap to your thumb, with the needle visible while holding a map in the same hand.

Best for: Orienteering competition where speed matters. The compass and map stay together in one hand, eliminating the time needed to bring a separate compass to the map for each bearing.

Not suitable for: Precise navigation, field use where deliberate bearing-taking matters, most survival and preparedness scenarios.

Models: Silva Thumb ($40-60), Suunto Orca ($60-80).

What to Look For (Baseplate)

When buying a navigation compass, minimum requirements:

• 2-degree graduation on the bezel: 5-degree graduation gives you less precision than you need for serious land navigation.
• Declination adjustment: A screw that offsets the orienting arrow to account for local magnetic declination. Without this, you either do mental math on every bearing or accept navigational error.
• Liquid-dampened needle: The needle should stop swinging within 3-4 seconds of disturbance. Cheaply made compasses oscillate for 10-15 seconds and never settle precisely.
• Romer/UTM scale: Engraved or printed scales on the base for measuring UTM grid coordinates directly from a map.
• Magnifier: Small magnifying lens in the base for reading fine map detail.

Optional but useful:

• Global needle: A needle balanced for use at any latitude. Standard needles are balanced for specific hemispheres.
• Clinometer: Measures slope angle (useful for avalanche assessment).
• Mirror sighting: A folding mirror behind the compass allows more precise bearing shots by letting you look at the needle and distant target simultaneously.

What to Avoid

• Fashion compasses: Any compass sold as jewelry or decorative gear, or included as a free gift with outdoor gear, is almost always useless for navigation.
• Unmarked bezels: If the bezel only shows N/S/E/W or 8-point markings, it's not a navigation compass.
• Bubbles in the housing: Air bubbles in the dampening liquid indicate previous damage (needle has been impacted) or manufacturing defect. A bubble causes imprecise needle behavior.
• Batteries or electronics: A compass with batteries can fail. A passive magnetic compass cannot.
• Incredibly cheap: Below $20, you get what you pay for. For a tool you may depend on for your life, buy from established compass brands (Suunto, Silva, Brunton, Cammenga).

Care and Storage

Keep compasses away from strong magnetic fields (speakers, motors, some magnets in clasps). A compass stored next to a strong magnet for an extended period can have its needle permanently demagnetized or reverse-polarized.

Check your compass against a known reference (another compass, a published declination map) annually. A reversed compass (south end points north) is worse than no compass because you'll confidently travel the wrong direction.