Square

Three signs apart, or 90 degrees, makes a square, a shape Ptolemy calls the quartile. In Ashmand's 1822 translation he classes it as discordant because it links signs of unlike kind. That is a geometric explanation, and Lilly 1659, who says harsher things of this aspect, gives no reason in that passage.

Not everyone accepted the verdict. Heindel 1919 calls the old scoring of good and bad aspects mistaken and compares hard aspects to the grinding of a gem, then says the stars give tendencies only. Modern popular astrology often describes a square as friction that gets things moving, closer to Heindel than to Lilly.

The calculator treats two bodies as square within 7 degrees either way. It reports only the angle, and whether that angle was a burden or a spur is the part the books never settled.