Mathematical indices describing metabolic control of the diabetic patients during a short-term (24 hours) monitoring period have been reviewed. Two groups of indices were selected: those related to the glucose level and those related to the glycaemia variations. Then a presentation of the most universal mathematical index, which is presently used in clinical practice, -M value - was performed. Due to certain discrepancies related to several versions of the M-index, an analysis of all variants (M80, M90, M100, M120) had been carried out. It was found that comparison of the M values calculated based on different glucose reference levels led to totally different results. Analysis indicated that for the considered profiles the best description of the glycaemic state can be obtained when levels of 80 mg/dl (M80) and 90 mg/dl (M90) are applied.