very convenient to draw a line when the notebook is not flat but the numbers quickly and disappear when the rule twists, it takes time to become flat. It's problematic because if you put the rule in your schoolbag and after you put lots of cabinets above, it wrongly and after, it's hard to draw lines. ATTENTION: for machouilleurs rule, it does not taste good. I recommend taking a flexible Maped rule but a little less than that.