We introduce a methodology for diagramming the ways students use sequences of mental actions to solve mathematical tasks. We studied 12 pre-service teachers as they solved a set of fractions tasks, ranked by cognitive demand. We present the unit transformation graphs for one of those pre-service teachers, to illustrate how she experienced and met cognitive demand across the fractions tasks. Specifically, the graphs illustrate how sequencing mental actions places demands on working memory and how units coordination structures can offload some of that demand. [For the complete proceedings, see ED629884.]