The plus and minus symbol (often called the plus/minus sign) is a mathematical sign used to show that the figure can be either a plus or a minus (negative) number. While you can quickly write this symbol manually, it may be harder to implement using a computer. There are two ways to insert the symbol in Mac OS X, depending on your Mac computer.
Check to see if you have the ± symbol on your Mac keyboard. Some Macbooks released in 2009 or later have the symbol on the keyboard above the "TAB" key. Press "Shift"+"§" to produce the "±" symbol. If you do not have this key, you can use the universal method.
Hold "Shift" and then hold "ALT" (Option).
Press the equals sign (=) key. The three-key combination will insert the ± symbol.