JEWELS OF A LODGE
Every Lodge is furnished with six jewels, three of which are movable and three immovable. They are termed jewels, says Brother Oliver, because they have a moral tendency which renders them jewels of inestimable value. The movable jewels, so called because they are not confined to any particular part of the Lodge, are the Rough .Ashlar, the Perfect Ashlar, and the Trestle-Board. The Immovable Jewels are the Square, the Level, and the Plumb. They are termed Immovable, because they are appropriated to particular parts of the Lodge, where alone they should be found, namely, the Square to the East, the Level to the West, and the Plumb to the South. In the English system the division is the reverse of this. There, the Square, Level, and Plumb are called Movable Jewels, because they pass from the three officers who wear them to their successors.
- Source: Mackey's Encyclopedia of Freemasonry