fixed costs tend to stay the same as volume of activity changes, or at least within a given volume range;
variable costs change as the volume of activity changes.
Fixed costs include things such as warehouse rental, which is charged on a time basis (/month). As volume of activity increases, additional warehouses may be added around Europe, and we get the familiar stepped fixed costs, as shown in Figure 3.3 opposite. The same relationship would apply if volumes were reduced and a warehouse closed.