Disclosed are methods, apparatuses, etc. for calibrating glucose monitoring sensors and/or insulin delivery systems. In certain example embodiments, blood glucose reference samples may be correlated with sensor measurements with regard to a delay associated with the sensor measurements. In certain other example embodiments, a blood-glucose concentration in a patient may be determined based, at least in part, on one or more probability models, one or more functions for estimating blood-glucose concentrations, and/or blood glucose reference sample-sensor measurement pairs.