unit-symbol index to clarify this dependency, as in {λ}m = 6.982 × 10−7 or equivalently {λ}nm = 698.2. In practice, where it is necessary to refer to the numerical value of a quantity expressed in a particular unit, it is notationally more convenient to simply divide the quantity through that unit, as in λ/m = 6.982 × 10−7 or equivalently λ/nm = 698.2. This is a particularly useful and widely used notation for labelling the axes of graphs or for the headings of table columns, where repeating the unit after each numerical value can be typographically inconvenient. Typographic conventions Symbols for quantities Quantities are generally represented by a symbol formed from single letters of the Latin or Greek alphabet. Symbols for quantities are set in italic type, independent of the type used in the rest of the text. If in a text different quantities use the same letter symbol, they can be distinguished via subscripts. A subscript is only set in italic type if it consists of a symbol for a quantity or a variable. Other subscripts are set in upright (roman) type. For example, write Vn for a "nominal volume" (where "n" is just an abbreviation for the word "nominal"), but write Vn if n is a running index number. Names and symbols for units If an internationally standardized symbol exists for a unit, then only that symbol should be used. See the SI articles for the list of standard symbols defined by the International System of Units. Note that the distinction between uppercase and lowercase letters is significant for SI unit symbols. For example, "k" is the prefix kilo and "K" stands for the unit kelvin. The symbols of all SI units named after a person or a place start with an uppercase letter, as do the symbols of all prefixes from mega on upwards. All other symbols are lowercase; the only exception is litre, where both l and L are allowed. However, it is stated that the CIPM will examine whether one of the two may be suppressed. Symbols for units should be printed in an upright (roman) typeface. Numbers See Sect. 3.3 of the Standard text. Numbers should be printed in upright (roman) type. ISO 31-0 (after Amendment 2) specifies that "the decimal sign is either the comma on the line or the point on the line". This follows resolution 10 of the 22nd CGPM, 2003.