Abstract: The operation of subtraction, though emphasized at the elementary level, has a central role in expressing foundational concepts in Calculus. In graphical representations of such concepts, interpreting the difference b–a as finding the distance between a and b often supports students in making sense of the representation. In this talk, I describe my research investigating how undergraduate students represent difference expressions on number lines. I detail four distinct representations observed in exploratory teaching interviews when students engaged with tasks designed to support them in using a “difference as distance between” representation of subtraction. I also discuss the ways in which each of the four representations may afford reasoning graphically about key results in Calculus. I close with implications for teaching and research as well as directions for future work.