Desmos is an excellent graphing calculator. Nick had a really great conversation with himself. The graphing calculator disagreed with the line that he had plotted. Which was correct? He oscillated between faith in himself and faith in his ipad, before spotting that 2 x 2 was not 2. Technology used as a self-marking tool can be powerful. To check at the end of the journey, rather than as an overly helpful crutch from the beginning of the journey.