Compass has a half-life of only about 12 years, so a compass that contains 120 mCi of tritium when new will contain only 60 when it is 12 years old, 30 when it is 24 years old, and so on. Consequently, the illumination of the display will fade. Mariners' compasses can have two or more magnets permanently attached to a compass card, which moves freely on a pivot. A "lubber line", which can be a marking on the compass bowl or a small fixed needle, indicates the ship's heading on the compass card. Traditionally the card is divided into thirty-two points
Points of the compass points such as north by east (NbE) between north and north-northeast, and northeast by north (NEbN) between north-northeast and northeast. A compass point allows reference to a specific course (or azimuth) in a colloquial fashion, without having to compute or remember degrees. The European nautical tradition retained the term "one point" to describe of a circle in such phrases as "two points to starboard". By the middle of the 18th century, the 32-point system was extended with half- and quarter-points to allow 128 directions to be differentiated. The names of the compass point directions follow these rules: In summary, the