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The double negative in Excel formulas
10 January 2019

In more advanced Excel formulas, you might run into the double negative operation (--).

The double negative (sometimes called the even more nerdy "double unary") coerces TRUE or FALSE values to their numeric equivalents, 1 and 0. It's used in formulas where numbers are needed for a particular math operation.

A double negative is not the only way to get ones and zeros from logicals. You can also add or subtract zero, multiply by one, or use the inscrutably named N function.

Full article: The double negative in Excel formulas