The Past Master Symbol is a often seen but not so frequently explained Masonic Symbol. It commonly consists of The Compass, Sun, and Quadrant (or Protractor), and in most jurisdictions a Square.
The Compass has a familiar interpretations for it is by the Compass that a Mason is reminded to keep his actions within due bounds. The Square also has a familiar meaning, for in Acting on the Square a Mason conducts himself honestly, with morality and virtue. The Square is the Master jewel (a reminder of how he should govern), and is a part of the Past Masters Symbol as a reminder of the office he held.
The Quadrant is the arc that the compass rests upon, either below or in place of the square on the familiar symbol of the fraternity. The Quadrant shows what angle the Compass is opened at. Symbolically, as every Mason is supposed to use the Compass to keep his actions within due bounds, it is The Quadrant that measures those due bounds,and it is the responsibility of the Master of the Lodge to ensure that Masons under his jurisdiction are making proper use of their own Compass. The Quadrant also shows the Compass to be opened to 60 degrees or the angle of an equilateral triangle, which is a symbol of balance.
The Compass paired with the Quadrant could also be seen as a Sextant a navigation tool used to measure altitude. The Sextant symbolizes that not only did the Past Master have to navigate the course of his Lodge in the past, but also that he is qualified to do so, should his successors require his advice or assistance.
The Sun represents Light and the Master of a Lodge is supposed to be a source of Masonic Light. It also signifies that the Past Master has observed the sun at meridian height (the South), setting (the West), and rising (the East).
In the some jurisdictions around the world, The 47th Problem of Euclid Suspended by a Square is used as The Past Master Symbol. The 47th Problem of Euclid (also known as the Pythagorean Theorem) is used to prove a square a vital skill to ancient builders. Suspended by the Square, the symbol represents the knowledge and wisdom that a Past Master has gained from his service to his Lodge and Masonry in general.
h/t – Bro. Kurt P.M of Hermes Lodge U.D