A student brings the remaining one sixth of a ruler to the point where his pencil previously stopped. The pencil goes down again, three centimeters of line gets drawn and the cycle repeats. The line is not particularly neat, nor was this method particularly fast. But the ruler was used.
My students almost always pull out rulers to draw lines. I never see a line drawn without the rulers coming out. Neat? Sure. Time consuming? Maddeningly. I just want to get on with the teaching. How about we connect the dots and move on to the next problem, shall we? The line does not have to be straight. And it probably will not be with a broken ruler. This is something that is difficult to teach. Just saying “Maybe it would be faster and just as neat to not use your broken ruler?” gets no response.
Perfect thing to think about with each task we do, though. What is necessary? What is slowing us down and not making our work better even though we hold on to it because it is precious?