A "Logical Value", also known as a "Boolean Value": has only two values in Excel: TRUE and FALSE.
Logical Values and Calculations
Logical values can also, in certain circumstances, be used in calculations.
When this occurs, Excel considers the logical values to be numbers,
TRUE is taken to have a value of one "1" and FALSE has a value of zero "0".
An example of using logical values in calculations can be seen in the image above where the logical values in cells F1 to F4 are added together in the formula:
= F1 + F2 + F3 + F4
Since TRUE is equal to 1 and FALSE equal to 0, the answer to the formula is 2.
= 1 + 0 + 1 + 0
Logical Values and Excel's Functions
As a result, the SUM function in the image above returns an answer of zero since it considers cells F1 to F4 to be blank.
To use logical values in functions such as SUM, the logical values must first be converted to numbers.