Tula is the seventh rashi, the Vedic sign of the balance or scales, corresponding to Libra. In jyotisha it is ruled by Venus (Shukra), and it is the sign of Saturn's exaltation, where Saturn is held strongest. Its quality is movable (chara), the cardinal mode, and its element is air (vayu tattva). Jyotisha reads Tula through Venus's sense of proportion and the scales' weighing: relationship, fairness, agreement, and the balancing of one against another. As a sidereal sign it is fixed to the stars and sits roughly 24 degrees behind tropical Libra. Venus's rulership and Saturn's exaltation here are dignities shared with Western astrology, and both traditions treat Tula as the sign most concerned with partnership and equilibrium.
Tula, balance, translates the Greek zygon, properly the beam or crossbar of a balance rather than the whole instrument, so the Sanskrit broadens the image slightly in naming the scales as a complete object; the transmission runs through the Yavanajataka, a versification of a Greek astrological text of roughly the second through fourth centuries CE, built in turn on the twelve equal signs Babylonian celestial divination had fixed by the fifth or fourth century BCE, a scheme absent from the older Vedic corpus entirely. Tula is also the only rashi named for a man-made object rather than a creature, a distinction it shares with the equivalent tropical Libra; Venus's rulership and Saturn's exaltation here belong to the later classical layer codified in compilations such as the Brihat Parashara Hora Shastra of roughly the seventh or eighth century CE.
Sources Brihat Parashara Hora ShastraSage Parashara (attributed) with The Yavanajataka of SphujidhvajaDavid Pingree, Jyotihsastra: Astral and Mathematical LiteratureDavid Pingree