In an example, a method includes forming a layer of build material and selectively applying fusing agent on to the layer based on a predetermined pattern. Energy may be applied to the layer of build material, and at least one temperature of the layer may be measured. A temperature distribution over the layer of build material may be determined, the temperature distribution indicating, for each of a plurality of locations on the layer of build material, whether fusing agent is present at that location. At least one characteristic derived from the temperature distribution may be compared to a predetermined characteristic. When the compared characteristics differ, an operational characteristic of an additive manufacturing apparatus may be adjusted.