A method of adjusting a watt density distribution of a resistive heater includes designing a baseline heater circuit. A detection circuit is designed having a constant trace watt density and the detection circuit overlaps the baseline heater circuit. The detection circuit is manufactured, and its baseline thermal map is obtained. The baseline heater circuit is manufactured, and a nominal thermal map is obtained. A subsequent detection circuit is manufactured, and an actual thermal map is obtained. A subtraction thermal image is created by subtracting the baseline thermal map from the actual thermal map, and a subsequent baseline heater circuit is modified according to the subtraction thermal image.