This calculator allows adjustment of temperature - emissivity measurements to another combination. It is convenient for IR thermometers that do not provide for adjustable emissivity.
The calculator does not do a lot of error checking, if you enter nonsense, it will produce nonsense. NaN means not a number, check the input values.
The results might be very sensitive to small changes in the input variables for some input data. It is worth doing a sensitivity analysis (by varying the input values by a small amount) to get some idea of the uncertainty.