Terminology: generic word for increase and decrease This is a really basic question. Consider a statement: > A painted line is increased by length $x$ Can $x$ be a negative number just by the wording of the question? What would be a better way of rephrasing the question, to make it clear that $x$ can be negative? (The reason I'm asking is that I'm programming and a method name needs to indicate that the parameter can be negative or positive, in order to decrease or increase a size) Basically I'm looking for a generic term for decrease and increase.

As a "neutral" verb regarding increase or decrease, I propose "adjust" so that the method would be `adjustLengthBy`. This is concise but conforms to the MS Code Complete dictum to use strong verbs in function names.