Fig. 2. A Clarke error grid for comparison points between continuous glucose-monitoring system and reference. Zone A: values differ from each other by no more than 20%. Zone B: values differ by more than 20% but do not result in an adverse treatment. Zone C: may result in overcorrection of an acceptable glucose value. Zone D: would not result in correction when, in truth, treatment should be administered. Zone E: would prompt inverse treatment. (Reproduced with permission from Piper HG, Alexander JL, Shukla A, Pigula F, Costello JM, Laussen PC, Jaksic T, Agus MS: Real-time continuous glucose monitoring in pediatric patients during and after cardiac surgery. Pediatrics 2006; 118:1176–84.)