Example LF.1.2 :$f(x) =x+2$.  "Added value": $2$
An arrow in the mapping diagram that starts at $x$ will end at the point, $x+2$, two units above the position $x$ on the target line.
Motion Interpretation: If $x$ is time and $f(x)$ is the position of an object on the target axis at time $x$, then at time $0$ the object is at position $2$. The position at time $x$ is is precisely $x$ units above (below)  $2$ when $x>0$ ($x<0$). The object is moving at a velocity of $\frac {\text {unit position}} {\text {unit time}}$.