Further separation of the volume variance component of a multi-product firm's revenue variance into mix and quantity variances is regularly advocated by management accounting educators. Techniques used to achieve this separation are generally an extension of the analytical techniques used in the traditional flexible budget step-down? approach to variance determination. The analysis in this paper suggests that such an extension in most multi-product situations is inappropriate and generates useless and misleading results. Specific situations in which relational (in lieu of mix) variances may be appropriate do exist and applicable techniques are developed.