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
Qibla compass Qibla compass A Qibla compass or qiblah compass (sometimes also called qibla/qiblah indicator) is a modified compass used by Muslims to indicate the direction to face to perform ritual prayers. In Islam, this direction is called qibla, and points towards the city of Mecca and specifically to the Ka'abah. While the compass, like any other compass, points north, the direction of prayer is indicated by marks on the perimeter of the dial, corresponding to different cities, or by a second pointer set by the user according to their own location. Al-Biruni wrote his book (Kitab Tahdid al-Amakin, or the demarcation