Square — 90°, orb 8°

Cardinal signs square other cardinal signs, except the one sitting opposite. The same pattern holds for fixed signs and for mutable signs, because those groups are spaced 90° apart around the ecliptic. The pairs of sign centers at exactly 90° are listed below. Gemini and Virgo are on that list: the two Mercury-ruled signs are a square, not a trine.

A 98° gap still matches, because 98 − 90 = 8. A 99° gap does not. The engine does not average this with a trine. Once the square matches, the pair is done.

Sign pages show two square rows each. Those rows are a property of the 30° grid. They are not a compatibility percentage. The birth chart applies the same 90°/8° test to actual planet longitudes, which are rarely sitting on the sign centers.

Worked numbers: 10° and 100° are exactly 90°, a square. 10° and 98° are 88° apart, inside the 8° orb. 10° and 81° are 71° apart, which misses both the sextile by 11° and the square by 19°, so the engine records nothing. Gemini’s center at 75° and Virgo’s center at 165° are the exact 90° case, and both are Mercury-ruled in this table. Sharing Mercury does not soften the square. The aspect function never looks at rulership.