Alchemy used a set of mostly standardized symbols, many of which were ligatures: 🜇 (AR, for aqua regia), 🜈 (S inside a V, for aqua vitae), 🝫 (MB, for "balneum Mariae" bath, a double boiler), 🝬 (VB, for "balneum vaporis", a steam bath), and 🝛 ("aaa", for amalgam). In astronomy, the dwarf planet Pluto is symbolized by a PL ligature, ♇. A different PL ligature, ⅊, represents the property line in surveying. In engineering diagrams, a CL ligature, ℄, represents the center line of an object.