A method for determining a set point for a thermal sensor. The method includes (a) distributing a layer of particulate material to provide a build bed surface; (b) depositing an amount of absorption modifier over a test region or a surrounding area; (c) heating the test region; (d) measuring a temperature value within the test region with the sensor; (e) distributing a new layer of material over the preceding layer; repeating (b) to (e) until the material of the test region starts to melt, wherein repeated step (b) deposits additional absorption modifier over the test region to absorb more energy from the heat source than the preceding layer; determining a set point for the thermal sensor from a characteristic in the evolution of the measured temperature value within the test region; and applying the set point to subsequent measurements of the thermal sensor.