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
Compass rose of the principal winds to come up with intermediate compass points, known as half-winds, at angles of difference of 22°. The names of the half-winds are simply combinations of the principal winds to either side, principal then ordinal. E.g. North-northeast (NNE), East-northeast (ENE), etc. 32-point compass roses are constructed by bisecting these angles, and coming up with quarter-winds at 11° angles of difference. Quarter-wind names are constructed with the names "X by Y", which can be read as "one quarter wind from X toward Y", where X is one of the eight principal winds and Y is one of the