Using the Plus-Minus Symbol
The plus-minus sign compresses two statements into one. In a measurement, 9.81 ± 0.02 m/s² means the true value lies somewhere between 9.79 and 9.83; in algebra, x = −b ± √(b² − 4ac) / 2a lists both roots of a quadratic at once; on an engineering drawing, 25 ± 0.05 sets a tolerance either side of the nominal dimension. Chess annotators use it too: ± after a move means White holds a clear advantage, while ∓ favours Black.
Spacing rules
Treat ± like a binary operator and put a normal space on each side: 3.2 ± 0.4, not 3.2±0.4. The exception is when the sign prefixes a lone number to mean "positive or negative", as in ±5 V, where it is attached. Scientific journals usually want the unit once, after the uncertainty (12.5 ± 0.3 kg), rather than repeated. When you write the uncertainty in parentheses instead, as 12.5(3) kg, the ± is dropped entirely.
± and ∓ together
The minus-or-plus sign ∓ exists so that a single line can carry two linked equations. In cos(a ± b) = cos a cos b ∓ sin a sin b, reading the top signs gives one identity and the bottom signs the other. Use ∓ only when it pairs with a ± elsewhere in the expression; on its own it is just a confusing way to write ±.
Typing and rendering
± is part of Latin-1, so it has a genuine Windows Alt code, Alt + 0177, and a Mac shortcut, Option + Shift + =. Phones hide it under the + key on the symbols page of both the iPhone keyboard and Gboard. In HTML the entity is ±, and in LaTeX the command is \pm, with \mp giving the inverted form. Every font that covers accented Latin letters includes the glyph, so it never turns into a box, and it survives copy-paste into spreadsheets, code comments and chat apps without being converted to an emoji. Some people type +/- or +- out of habit, which is fine in plain-text email but looks unprofessional in a report and is harder for a screen reader, which announces the real character as "plus or minus".
Everyday and social uses
Outside science, ± shows up in fitness posts ("±10 kg this year"), in price estimates and in bios as shorthand for "give or take". Pair it with the infinity symbol or the not equal sign for a maths-flavoured aesthetic, or drop it between words styled with the small fonts generator for a subtle divider that reads as text rather than decoration.