Non-magnetic compass comprising a movable prism mounted above a display surface

Claim 1

IN COMBINATION WITH A SOURCE OF LIGHT, A PRISM HAVING A PLURALITY OF INPUT AND OUTPUT SIDES EQUAL IN NUMBER TO A MULTIPLE OF FOUR FACING DIFFERENT DIRECTIONS RELATIVE TO A CENTRAL AXIS, MEANS POSITIONING THE PRISM ABOUT A POSITIONING AXIS IN NON-SYMMETRICAL RELATION TO THE SOURCE OF LIGHT FOR REFRACTION OF LIGHT ENTERING SAID INPUT SIDES, AND DISPLAY MEANS MOUNTED IN SPACED RELATION TO THE PRISM FOR PRESENTING A SPECTRAL PATTERN ON A SURFACE PARALLEL TO SAID POSITIONING AXIS PRODUCED BY REFRACTED LIGHT EMERGING FROM THE OUTPUT SIDES OF THE PRISM WHICH PATTERN IS ELONGATED IN ONE DIRECTION RELATIVE TO A CENTER DEFINED BY THE INTERSECTION OF SAID CENTRAL AXIS WITH THE SURFACE, SAID INPUT SIDES BEING PLANAR FACES OF AN EQUILATERAL PYRAMID CONVERGING IN A DIRECTION AWAY FROM THE DISPLAY MEANS IN SUMMETRIC RELATION TO THE CENTRAL AXIS, SAID OUTPUT SIDES OF THE PRISM BEING EQUAL IN NUMBER TO THE INPUT SIDES AND BEING PLANAR FACES OF AN EQUILATERAL PYRAMID TRUNCATED PERPENDICULAR TO SAID CENTRAL AXIS AND CONVERGING TOWARD THE DISPLAY MEANS.