# How a Compass Works Part of the Orienteering Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/orienteering/guide/index.md) *3. Compass Skills* > **3a.** Explain how a compass works. Describe the features of an orienteering compass. Pick up a compass and the needle swings, wobbles, and settles — pointing roughly north every single time. It does this without batteries, without satellites, without any signal at all. Understanding *why* is the first step to trusting this tool with your navigation. ## How a Compass Works The Earth has a magnetic field generated by molten iron circulating in its outer core. This field extends from the South Magnetic Pole to the North Magnetic Pole, creating invisible lines of force that wrap around the planet. A compass needle is a small, lightweight magnet balanced on a nearly frictionless pivot. It aligns itself with the Earth's magnetic field, so one end (usually painted red) points toward magnetic north. That is the entire principle: a free-spinning magnet aligns with the Earth's magnetism. No moving parts except the needle itself, no power source, no signal required. This is why a compass works in canyons where GPS fails, in storms where satellites are blocked, and in remote wilderness where there is no cell service. > **Did You Know?** > > The Earth's magnetic north pole is not fixed — it wanders about 55 kilometers per year. Right now it is moving from the Canadian Arctic toward Siberia. This means compass declination values printed on older maps may be slightly off. ## Parts of an Orienteering Compass An orienteering compass (also called a baseplate compass) is specifically designed for use with a map. It has features you will not find on a simple pocket compass. ![Labeled diagram of a baseplate orienteering compass showing all major parts: baseplate, direction-of-travel arrow, index line, rotating bezel with degree markings, orienting arrow, orienting lines, magnetic needle with red north end, magnifying lens, and ruler markings](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/orienteering/guide/orienteering-compass-parts?v=c8aecc4b) ### Baseplate The flat, transparent plastic base that the compass housing sits on. Transparency matters — you need to see the map through it. The baseplate has a **direction-of-travel arrow** printed on it, a straight edge for drawing lines on maps, and ruler markings (usually in millimeters and map scales) along the edges. ### Rotating Bezel (Housing) The circular dial marked with degrees from 0° to 360°. You twist it to set your bearing. The **index line** (or read bearing mark) is where the bezel meets the direction-of-travel arrow — this is where you read your bearing number. ### Magnetic Needle Floating inside the bezel on a jeweled pivot, the needle spins freely and points to magnetic north. The north end is usually red. Some needles have luminous markings for use in low light. ### Orienting Arrow and Lines Inside the bezel (printed on the bottom of the housing), you will find the **orienting arrow** — sometimes called the "shed" or "doghouse" because of its shape. Surrounding it are **orienting lines** (also called meridian lines) that run parallel to the arrow. When you rotate the bezel, these move with it. Their job is to align with the north-south lines on your map. ### Ruler and Scale Markings The baseplate edges have rulers — typically in millimeters, plus one or two common map scales (1:25,000, 1:10,000). These let you measure distances directly on the map without a separate ruler. > **Tip** > > When buying an orienteering compass, look for one with a **liquid-filled housing** (the needle settles faster), a **clear baseplate** (easier to read the map through), and **luminous markings** on the needle (useful for night orienteering). Avoid cheap compasses with sticky needles or small baseplates. ## Types of Compasses While the baseplate orienteering compass is what you will use for this badge, it helps to know the other types exist: - **Thumb compass** — Straps to your thumb. Preferred by competitive orienteers because it keeps the map and compass in one hand. Faster but takes practice. - **Lensatic (military) compass** — Heavy, precise, and built for durability. Used by the military for detailed land navigation but slower to use with a map. - **Button (pocket) compass** — Small and cheap. Fine for general direction but lacks the features needed for orienteering. Video: [Basic Orienteering Skills](https://www.youtube.com/watch?v=bzNA6-lx5n8) > **Be Prepared! Your Compass Needle Isn't Settling** > > You pull out your compass and the needle wobbles endlessly instead of settling on north. What do you do? > > - **Check for metal.** Move away from belt buckles, zippers, vehicles, power lines, and metal fences. Even a steel watch or phone in your pocket can deflect the needle. > - **Hold it level.** If the compass is tilted, the needle may drag against the housing. > - **Check for bubbles.** A small bubble in a liquid-filled compass is normal and does not affect accuracy. A large bubble may mean the housing is cracked. > - **Try a different location.** Some rocks contain magnetic minerals (like magnetite) that create local magnetic anomalies. --- - Previous: [What Is Orienteering?](https://merit-badge.university/merit-badges/orienteering/guide/req2/index.md) - Next: [Taking a Compass Bearing](https://merit-badge.university/merit-badges/orienteering/guide/req3b/index.md)