1. A system configured to determine a future disease control value comprising: a measuring device configured to record a plurality of measured disease control values; a memory configured to store (i) a plurality of optimal disease control values at a plurality of times, (ii) a plurality of optimal self-care values of a patient at said times, (iii) said plurality of measured disease control values at said times, and (iv) a plurality of self-care values at said times; and a processor unit configured to read from the memory, said processor unit programmed to (A) generate a plurality of scaling factors customized to said patient in response to changes in any one of said self-care values or said measured disease control values at any one of said times and (B) calculate the future disease control value based on (i) a plurality of differentials, one of said differentials calculated as one of the scaling factors multiplied by first differences between one of the self-care values and one of the optimal self-care values, (ii) a sum of the differentials plus, (iii) a second difference between one of the measured disease control values and a corresponding one of the optimal disease control values and (iv) an addition of the second difference to the sum of the differentials.