The two basic parameters traditionally employed in qualitative phase identification using the powder diffractometer are the diffracted peak maximum intensity and the interplanar spacing “d”. Moat routine powder diffractometry carried out today is performed with the parafocussing geometry, and this arrangement gives a diffraction pattern in terms of diffraction angle (2-theta) vs. intensity. During the course of obtaining a set of experimental 20 and intensity values from a specimen to be analysed and in the subsequent conversion of these data to a d/I list for qualitative phase identification, errors will of course accrue. Most qualitative search methods in use today give high credence to the d-value, since this is by far the most accurately known of the two search parameters, and d-values of a few tenths of a percent are reasonably easily obtained with a well aligned and properly calibrated diffractometer. Intensities, on the other hand, can be subject to errors of the order of tens of percent, and problems arise in qualitative analysis where the need arises to subtract an identified phase from a multi-phase pattern to allow identification of further phases.