Purpose of -- in SUMPRODUCT?

[The Shaffer s]

In several threads, I see the use of "--" before the arguments to SUMPRODUCT
function and was wondering what purpose a double-negative serves.

Ken shaffer

 

[Myrna Larson]

Where you see the --, it's in front of a formula that returns TRUE or FALSE.
SUMPRODUCT ignores TRUE/FALSE values. The -- converts the TRUE to 1 and FALSE
to 0.

 

[Ryan Poth]

It forces a boolean (True/False) result to be analyzed as a numeric (1/0)
value.

 

[JE McGimpsey]

See

http://www.mcgimpsey.com/excel/doubleneg.html