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 equivalence theorem only a collapsing compass and no straightedge. There are several proofs of the correctness of this construction and it is often left as an exercise for the reader. Here is a modern one using transformations. Compass equivalence theorem The compass equivalence theorem is an important statement in compass and straightedge constructions. The tool advocated by Plato in these constructions is a "divider" or "collapsing compass", that is, a compass that "collapses" whenever it is lifted from a page, so that it may not be directly used to transfer distances. The "modern compass" with its fixable aperture can be used to