 3. The M-value is a quantitative index of the lack of treatment efficacy of an individual patient. The index describes both mean glycemic control and glucose excursions. The M-value is a logarithmic transformation of the deviation from an arbitrary standard selected by the physician that gives extra weight to hypoglycemic values. The original concept of Schlichtkrull et al. 19653 has been modified by Service et al. 1970 4 into the formula: 