Conceptualisations of slope based on mathematics education literature. [1] S. Stump, "Developing preservice teachers’ pedagogical content knowledge of slope", The Journal of Mathematical Behavior, vol. 20, no. 2, pp. 207–227, 2001a. [2] D. Moore-Russo, A. Conner, & K.I. Rugg, "Can slope be negative in 3-space? Studying concept image of slope through collective definition construction", Educational Studies in Mathematics, vol. 76, no. 1, pp. 3-21, 2011.