Clear Base Plate

• Most compasses now have a clear, rectangular base plate that holds the housing and dial in the center. It also has rulers and a direction of travel arrow etched on it. This helps to get a more accurate reading. Some base plates also have a small magnifying circle as well for use when deciphering tiny features, words or contour lines on maps.
  
  

Housing and Dial

• The circular, rotatable housing for the needle is filled with liquid that reduces vibrations of the needle and increasing accuracy. The dial on the housing is marked in degrees from 0 to 360.
  
  

Meridian Lines and Orienteering Arrow

• These are located beneath the needle and are used for alignment.
  
  

Optional Features

• Some compasses have an adjustable declination arrow which costs a bit more but helps to correct for magnetic declination. Some compasses also have a clinometer which measures slope and some have a hinged cover with a sighting mirror and lanyard.
  
  

Quality

• Top of the line compasses have all these features. Small, cheap compasses without base plates are not recommended for real backcountry and mountaineering use. They will not work well with maps and are not as reliable.