In Ladd, D. R., & Morton, R. (1997), the authors write:
It is customary to think of an intonation contour as having a linguistically distinctive shape or pattern and an independently variable pitch range. In a one-word English utterance, we may have any one of a handful of distinctive contour shapes— signalling that the contour is, for example, a question or a statement—and any of these shapes may be realized with more or less any pitch range or ‘‘vertical scale’’
Later, they clarify what they mean by "vertical scale":
But even in the case of pitch range effects that convey some kind of linguistic meaning, such as different degrees of emphasis, it still seems appropriate to distinguish them from the shape of the contour, and to treat them as orthogonal (as the ‘‘vertical scale’’ metaphor suggests).
But what am I to understand by "vertical scale", exactly? The f0 height with which an intonation contour is realized?
CITED 1. Ladd, D. R., & Morton, R. (1997). The perception of intonational emphasis: continuous or categorical? Journal of Phonetics.