XXX). This usage has also been inconsistent. Specific disciplines In astronautics, United States rocket model variants are sometimes designated by Roman numerals, e.g. Titan I, Titan II, Titan III, Saturn I, Saturn V. In astronomy, the natural satellites or "moons" of the planets are designated by capital Roman numerals appended to the planet's name. For example, Titan's designation is Saturn . In chemistry, Roman numerals are sometimes used to denote the groups of the periodic table, but this has officially been deprecated in favour of Arabic numerals. They are also used in the IUPAC nomenclature of inorganic chemistry, for the oxidation number of cations which can take on several different positive charges. They are also used for naming phases of polymorphic crystals, such as ice. In education, school grades (in the sense of year-groups rather than test scores) are sometimes referred to by a Roman numeral; for example, "grade " is sometimes seen for "grade 9". In entomology, the broods of the thirteen and seventeen year periodical cicadas are identified by Roman numerals. In graphic design stylised Roman numerals may represent numeric values. In law, Roman numerals are commonly used to help organize legal codes as part of an alphanumeric outline. In mathematics (including trigonometry, statistics, and calculus), when a graph includes negative numbers, its quadrants are named using , , , and . These quadrant names signify positive numbers on both axes, negative numbers on the X axis, negative numbers on both axes, and negative numbers on the Y axis, respectively. The use of Roman numerals to designate quadrants avoids confusion, since Arabic numerals are used for the actual data represented in the graph. In military unit designation, Roman numerals are often used to distinguish between units at different levels. This reduces possible confusion, especially when viewing operational or strategic level maps. In particular, army corps are often numbered using Roman numerals (for example the American XVIII Airborne Corps or the WW2-era German III Panzerkorps) with Arabic numerals being used for divisions and armies. In music, Roman numerals are used in several contexts: Movements are often numbered using Roman numerals. In Roman Numeral Analysis, harmonic function is identified using Roman Numerals. Individual strings of stringed instruments, such as the violin, are often denoted by Roman numerals, with higher numbers denoting lower strings. In pharmacy, Roman numerals were used with the now largely obsolete apothecaries' system of measurement: including to