Ruler ... See neighboring photos. Especially this one. Why manufacturers seem to be STUPID, INCOMPETENT, or both.
I originally took the picture as part of a worksheet to help my students distinguish between imperial and metric measurement. Now I look at it as a symbol of incompetence of ruler manufacturers. My students are regularly confused by this sort of marking, thinking that the numbered intervals are mm. Usually these same rulers mark the other side as "inches" and the inches are numbered. So why do they mark the metric side "mm" when the centimeters are numbered??!!
I'd rather they put cm after the number 1, and shrink the mm and nestle it down next to the mm markings, between zero and 5mm. The way they have it is just too ambiguous, especially for people who struggle with the metric system.
For the life of me, I cannot figure out why this picture has more than a couple of views. I put it up more as a joke. If you feel like it, let me know why you are looking at it.