We define classical exponents of Diophantine approximation attached to real matrices and state various transference theorems between them. We show how the parametric geometry of numbers, introduced by Schmidt and Summerer and further developed by Roy, allows us to give an easy proof of these transference theorems. Furthermore, we explain how this recent theory can be applied to determine the spectra of several exponents of Diophantine approximation (that is, the set of values they take on real entries).