• Yes, I agree. The explanation is incorrect.

    To further illustrate what is happening here, try substituting =+ with =-

    My interpretation is that you are applying a positive modifier to a negative value,

    which obviously results in a negative return. If you apply a negative modifier to a negative number, the result is positive.

    select @a =- @b-2

    will return +21 when b is -21

    😉