Symbols that function as notation rather than as pictures — each stands for a precise quantity, relation or unit, and each was deliberately introduced by an identifiable person or standards process rather than evolving through cultural use. That origin is what separates them from the rest of the catalogue: their meanings were defined, not inherited, and can be traced to a specific proposal.
Two short horizontal parallel lines (=), denoting that the values on either side are equal.
A sideways figure-eight (∞) denoting an unbounded quantity in mathematics, and used more broadly as a symbol of endlessness.
The horseshoe-shaped capital letter used to denote the ohm, the SI unit of electrical resistance — visually identical to, but formally distinct from, the Greek letter omega.
The mathematical sign for addition, written as an upright cross.
The mathematical sign for subtraction, written as a single horizontal stroke.
The diagonal cross used to indicate multiplication.
A horizontal stroke with a dot above and below, indicating division.
A plus sign above a minus stroke, giving a tolerance or two possible values.
Two small circles either side of a diagonal stroke, meaning 'per hundred'.
A percent sign with an extra circle, meaning 'per thousand'.
The Greek letter used for the ratio of a circle's circumference to its diameter.
A hooked stroke with a horizontal bar, indicating a root of a number.
The capital Greek sigma, used to indicate a sum over a series.
An elongated S indicating integration in calculus.
A rounded d with a curled top, marking differentiation in one variable.
A small raised circle marking degrees of temperature, angle or arc.
An equals sign struck through by a diagonal stroke, meaning inequality.
Two stacked wavy strokes, meaning 'roughly equal to'.
Three dots in an upward-pointing triangle, introducing a conclusion.