It performs simple subtraction, addition, and average of signals in the two images.

It's more than just simple subtraction of the total aid from the total cost and making it to zero.

So simple subtraction from one hundred eighty gives me angle remaining, and I have thus described triangle perfectly, except for dimension of sides.

"In a case of even the simplest subtraction," Hélène had said, "you've got to know what you're trying to subtract from."