In many schoolbooks, students mainly interpret ready-made graphs (Friel et al., 2001; Moritz, Chapter 10). And if students have to make graphs, the goal is too often just to learn how to produce a particular graph. De Lange, Burrill, Romberg, & van Reeuwijk (1993) and Meira (1995) strongly recommend letting students invent their own graphs. We may assume that students’ own graphs are meaningful and functional for them.