When you type an equal sign into an empty cell, Excel assumes that you are entering a formula (a formula always begins with an equal sign). Excel's accommodating nature also permits you to begin your formula with a minus sign or a plus sign. However, Excel always inserts the leading equal sign after you enter the formula.

As a concession to former 1-2-3 users, Excel also enables you to use an @ symbol to begin a formula that stars with a function. For example, Excel accepts either of the following formulas:

=SUM(A1:A200)

@SUM(A1:A200)

However, after you enter the second formula, Excel replaces the @ symbol with an equal sign.