One of Prof. Castaing’s most important gifts to the field of X-ray microanalysis was his insight that quantification could only effectively be carried out by procedures which relied on measurements relative to a suitable standard, because in this way is was the functional variation, rather than the absolute value, of most quantities that had to be known or approximated. At the time this was seen to be a necessary step because the state of knowledge about the fundamental parameters of electron solid interactions was regarded as poor. in the intervening fifty years this situation has not changed very much. Even more unfortunately the kinds of problems to which electron beam microanalysis is now applied - such as the analysis of highly inhomogeneous or very small samples - are of such a nature that quantitative methods based on standardization are no longer feasible.