Some Suunto mechanical compasses are with a mirror installed on a hinged lid. With the lid open, the mirror reflects your compass.
The primary reason for having a mirror compass is to be able to sight a direction or an object with the compass capsule visible at the same time. This is done by opening the mirror to approximately 45 degrees. At this angle, you can see in the mirror the object aligned with the sighting aids of the compass, as well as the compass capsule and protractor, when lifting the compass to the level of your eyes roughly at arm’s length.
A mirror also enables signaling over long distances by flashing sunlight reflected in the mirror. To know where the reflected light is directed, use two fingers in a V-shape at arm’s length so that you see the target between your fingers. Then, keep the open compass mirror upright close to your eyes and turn the mirror until the reflected sunlight hits your fingers. Then, by rotating the mirror left-to-right, you can create a flashing signal in the desired direction.
With the mirror lid fully opened you have a longer straight line for determining direction of travel and for working on the map. The mirror lid and baseplate are always aligned in Suunto compasses for this purpose. The mirror lid also provides extra protection when closed and stowed away. The mirror and lid are made of impact resistant materials, ideal for outdoor exploration.
Some Suunto mirror compasses include a clinometer in the form of a weighted needle that moves independently of the compass needle when holding the compass on its side.
You can measure the slope by aligning the lower edge of the compass with the slope or by sighting an object above or below you with the aid of the mirror. When using the clinometer needle the compass must be tilted on its long edge and the capsule turned so that the 0 on the declination scale points towards the edge pointing down. The angle in degrees can then be read from the declination scale inside the compass capsule from where the weighted needle is pointing.