The internal temperature sensor must be calibrated on each device before it can effectively be used.
Two calibrations methods can be used: 1 point or 2 point.
At least a 1-point calibration is needed. Without this calibration, the offset of the internal temperature sensor is not known. After the offset is known, the coefficient (35.7) can be applied to determine the temperature. The coefficient is basically a sloped line on a graph, and the offset places the line somewhere vertically.
A 2-point calibration determines not only the offset but also the slope. This calibration can be done if higher accuracy is required over a greater temperature range.