Plus–minus sign
Other meanings occur in other fields, including medicine, engineering, chemistry, electronics, linguistics, and philosophy.The above expression can be rewritten as x ± (y − z) to avoid use of ∓, but cases such as the trigonometric identity are most neatly written using the "∓" sign: which represents the two equations: Another example is the conjugate of the perfect squares which represents the two equations: A related usage is found in this presentation of the formula for the Taylor series of the sine function: Here, the plus-or-minus sign indicates that the term may be added or subtracted depending on whether n is odd or even; a rule which can be deduced from the first few terms.If a brief, simple description is not possible, the equation must be re-written to provide clarity; e.g. by introducing variables such as s1, s2, ... and specifying a value of +1 or −1 separately for each, or some appropriate relation, like s3 = s1 · (s2)n or similar.The use of ± for an approximation is most commonly encountered in presenting the numerical value of a quantity, together with its tolerance or its statistical margin of error.Operations involving uncertain values should always try to preserve the uncertainty, in order to avoid propagation of error.