This paper makes three contributions to the discussion of vowel transformation in acoustic phonetics. Firstly, it compares a selection of transformation routines, using three performance tests: Linear Discriminant Analysis of vowel categories, inter-speaker vowel space area homogenisation, and inter-speaker vowel space overlap. Secondly, the complementary functions of psychoacoustic transformation and speaker-dependent normalisation proper are discussed and demonstrated. And, thirdly, multi-dimensional scaling is proposed as a tool that can be useful in the assessment of multi-dimensional (or multi-parametric) results common in the testing of different methodologies, but also in other experimental work.