Imagine walking along the number line from a starting point \(A\) to a final point \(B\text{.}\) The difference \(B-A\) is called the displacement from \(A\) to \(B\text{,}\) or the deviation of \(B\) from \(A\text{.}\) In words, the deviation of \(B\) from \(A\) is how far \(B\) is from \(A\) on the number line, with the directional information indicated by a plus or minus sign. If \(B\) is less than \(A\) (this is the same as \(B\) being to the left of \(A\) in the standard orientation of the number line), then the deviation of \(B\) from \(A\) is negative. Likewise, if \(B\) is greater than \(A\) (or \(B\) is to the right of \(A\) in the standard orientation of the number line), then the deviation of \(B\) from \(A\) is positive. Finally, if \(B=A\text{,}\) then the deviation of \(B\) from \(A\) is zero. See Figure Figure 1.3.1.
