Penalty index as a function of blood glucose (BG). Each BG observation corresponds to a penalty. The dashed line represents the staircase penalty index function (here, the penalty is denoted as ρ). For reasons explained in the text, this staircase function was transformed into a more smoothed penalty index function, which is illustrated by the solid line. The penalties are symbolized by β, γ, and δ for the low, normal, and high BG measurements, respectively. The 'clinically acceptable' cut-off glycemic penalty index (GPI) equals 23 and corresponds to a 'clinically acceptable' BG range of 74–120 mg/dl. The target normoglycemic range, however, remains 80 to 110 mg/dl with a corresponding penalty value equal to 0.