Apparatus, method, system and kit for receiving a plurality of continuous analyte sensor values for corresponding reference analyte values, calculating a rate of change value for the continuous analyte sensor values, defining a plurality of data range windows of the reference analyte values, evaluating the corresponding continuous analyte sensor values, the rate of change values, the reference analyte values, and/or a plurality of corresponding difference values for the plurality of data range windows, and determining a best fit based on the evaluation of the plurality of data range windows are provided.