This paper addresses one example of quantitative spectroscopy which plays a crucial role in the assessment of the fusion reaction between deuterons and tritons, that is the measurement of the plasma ion temperature and its radial profile. Closely related to this is the measurement of the deuteron density, both quantities provided by active beam charge exchange spectroscopy. In spite of the progress, and the development of numerous analytic tools over the last decade, there remain a number of important problems. Some of these have yet to be formulated completely whilst others await the results of further modelling, in particular of the plasma edge. Some examples are given in this paper, in particular comparisons of impurity ion temperatures, high ion temperatures at the plasma boundary, the role of temperature fluctuations, and finally anisotropic temperatures in neutral beam fuelled plasmas