Kindle as a ruler

I forgot to bring my main ruler with me to Mathematics class this afternoon. As it turned out, on one of the tests the class had today there were two graph questions, one of which required a ruler and the other it was useful - but not explicitly necessary - to have one on hand. In my ruler's place, I used my Kindle instead; this wasn't a wise idea because my pen slipped, went under my Kindle and I drew a line in the wrong place.

Fortunately, my stapler worked as an adequate substitute for my ruler and I did not lose any marks for any poorly drawn lines; instead, I think I might have lost marks for providing an incorrect answer to one or two of the questions related to the graph! On the bright side, I think I performed well on the test overall, which is what counts; I can improve on the parts where I went wrong.