I believe GP was referring to delta as in mathematics, which refers to difference and not necessarily change. So the delta between +7km/s and -7km/s is 14km/s.

I believe GP was referring to delta as in mathematics, which refers to difference and not necessarily change. So the delta between +7km/s and -7km/s is 14km/s. You are technically correct, though based on common usage patio11 got their point across.