No parallax error : a prism projects the reading of the bearing to infinity. This also contributes to a more comfortable operation, as you do not need to alternate close-reading to read the card and infinite-reading to take bearings. Optimum conditions to take bearings, thanks to the superb card stability and the wide 20° field of view, which will accommodate the roughest sea conditions. Most accurate bearing : the pivot and very hard stone are a guarantee of long life and shock resistance of your compass. Soft bottom cell : engineered using ultra-sonic welding, it acts like an expansion diaphragm, preventing the formation of bubbles and leaks. Built-in photoluminescent lighting, completely maintenance-free, impervious to corrosion, operates without batteries or radio-active tritium. Course reading from above the compass : you can read your compass like a standard compass, with no need to look through the prism. Military and field compass applications : Army green (ref. 63873) and Sand (63603) models are available on special request with MILS graduation. Graduation in MILS MILS : . Direct reading every 400 MIL . Reading through prism every 200 MIL.