The sign of Gemini is divided into five unequal terms, or bounds, in the Egyptian table of planetary terms transmitted by Vettius Valens in his second century Anthologies and recorded by Claudius Ptolemy in the Tetrabiblos, Book I. Running in degree order from the start of the sign, Gemini's five terms are ruled in this sequence: Mercury (0-6), Jupiter (6-12), Venus (12-17), Mars (17-24), Saturn (24-30).
Ptolemy's own discussion in the Tetrabiblos presents the Egyptian table alongside at least one rival term system, sometimes called the Chaldean, and Ptolemy proposes his own revised set of boundaries distinct from both, a three-way divergence that later Hellenistic and medieval astrologers continued to debate. The table this atlas follows for Gemini and the other eleven signs is the Egyptian version Valens transmits, which remained the version in ordinary use among Hellenistic astrologers long after Ptolemy raised his own objections to it.
Within Gemini the widest term belongs to Mars, spanning 7 degrees, and the narrowest to Venus, spanning 5 degrees, an unevenness that holds across all twelve signs in the Egyptian table: no sign's five terms are ever divided equally, and the five ruling planets, the five visible to the naked eye rather than the sun and moon, are distributed sign by sign rather than in one fixed order repeated throughout the zodiac.