! mathematics The factorial expression, i.e. 2! equals the product 2 × 1, 3! = 3 × 2 × 1, etc.
!! mathematics The double-step factorial expression, i.e. 3!! equals the product 3 × 1, 5! = 5 × 3 × 1, etc., used in radiative transition probabilities.
[Weisskopf V. F. Phys. Rev. Ser. 2 Vol. 83, 1073 (1951)]
″ See second.
# The ‘numero’ symbol, used widely in North America as a prefix for both an identifying number and a numeric count; because it replaces the £ sign on many keyboards, it is often called ‘pound’.
% See percentage.
′ See prime.
(g)2 See square grade.
(°)2 See square degree.
* A multiply symbol, e.g. a*b means a multiplied by b.
** An exponentiation symbol, e.g. a**b means a to the power b.
+ The ‘plus’ symbol, applicable to the addition operation and simple signage (where it is usually omitted, implicit).
, Used in British tradition to punctuate integers, at every third position left-wards from the decimal point, but used in European practice as the decimal point. Consequently abjured within this text in favour of the space character (which is used likewise to punctuate the fractional part).
- The ‘minus’ symbol, applicable to the subtraction operation and simple signage. See negative number for form with logarithms.
. Identically the ‘full stop’ of British tradition and the ‘period’ of North America, now universally also the ‘dot’, but also the ‘decimal point’ used in English-speaking practice for separating integer and fractional parts of a number, even of a non-decimal number. Used likewise in this text.
: The ratio symbol.
∧ Used in emails and some other typographically constrained situations as an exponentiation symbol, e.g. a∧b means a to the power b.
/ Called ‘solidus’ properly but ‘slash’ vernacularly, it is used as a ratio or divider symbol, including within the formalities of the SI, e.g. a/b means a divided by b.
˜ The ‘tilde’ of Spanish orthography; used within this text, in a lowered position, to represent further unstated digits in a number.
‰ See permille, i.e. parts per thousand, akin to percentage.
° See degree; for (°)2 see square degree.
• Historically the decimal point of British practice, now a multiply symbol, e.g. a·b means a multiplied by b.
∞ See infinity.
|z| See modulus.
□° See square degree.
α sub-atomic physics See fine-structure constant.
γ [Etymology: Gk letter ‘g’, its name Anglicized as gamma] See Newtonian gravitational constant.
mass (Metric) Old symbol for microgram, now properly μg.
γe sub-atomic physics Electron gyromagnetic ratio. See electron.
γn sub-atomic physics Neutron gyromagnetic ratio. See neutron.
γp electromagnetics Proton gyromagnetic ratio. See proton.
ɛ0 sub-atomic physics See electric constant.
ϕ [Etymology: Gk letter ‘f’, its name Anglicized as phi] mathematics See golden ratio.
geology Relates to phi scale; see particle size.
Φ0 electromagnetics See magnetic flux quantum.
λ [Etymology: Gk letter ‘l’, its name Anglicized as lambda] length See lambda.
volume (Metric) Old symbol for microlitre, now properly μL.
sub-atomic physics Bohr magneton; see magneton.
λC sub-atomic physics See Compton wavelength.
sub-atomic physics See Compton wavelength.
μ [Etymology: Gk letter ‘m’, its name Anglicized as mu, pronounced ‘mew’] (Metric) Official symbol for the prefix micro-, i.e. for 10-6. Originally adopted to mean the micron, i.e. the micrometre (10-6 m). Sometimes represented by the μ untouched - a deprecated practice. Often substituted by mc- with microgram in North America; see mcg.
μ0 electromagnetics See magnetic constant.
μB sub-atomic physics Bohr magneton. See magneton.
μb pressure An improper representation of microbar.
μd sub-atomic physics Deuteron magnetic moment. See deuteron.
μEq Microequivalent. See equivalent weight.
μe sub-atomic physics Electron magnetic moment. See electron.
μN sub-atomic physics Nuclear magneton. See magneton.
μn sub-atomic physics Neutron magnetic moment. See neutron.
μP sub-atomic physics Proton magnetic moment. See proton.
μμ (Metric) Old symbol for millimicron.
π (pi) [Etymology: Gk letter ‘p’, its name Anglicized as pi, pronounced ‘pie’] See pi.
σ [Etymology: Gk letter ‘s’, its name Anglicized as sigma] See sigma.
See
standard deviation.
fundamental physical constants See Stefan-Boltzmann constant.
See also stigma; symmetry number.
σe sub-atomic physics See Thomson cross-section.
Ω [Etymology: Gk letter ‘O’, the final letter of that alphabet, its name Anglicized as omega] electromagnetics (Metric) Official symbol for ohm. Also prefixed, as in mΩ = milliohm; see SI alphabet.
ℵ [Etymology: The first letter of the Hebrew alphabet, its name Anglicized as aleph.] See infinity.