Modal logic ruler

thingiverse

This is designed for use with a standard pencil and works great when used with one. I've tried using it with a mechanical pencil, and while it worked fine, the spaces were slightly too wide. It doesn't work at all with a ballpoint pen in my experience. A very minimal ruler that I created for my modal logic class. It can either draw a modal double scope line for possibility elimination and modal implication introduction, or you can simply use the box and first line for a quick necessity introduction. Finally, the single vertical and horizontal lines by themselves can create a non-modal assumption scope. During the course, one of the most repeated patterns I ended up drawing was the double modal scope line. It takes quite a lot of movements to draw it correctly, first you have to move the ruler slightly away from the first line, but not too far away, then you have to draw the horizontal line. All these steps add up if you're writing a test or just want to draw them neatly over and over again in a quick way. Another minor annoyance when using a standard ruler is deciding how long you want your lines to be. After doing a couple of proofs with a standard ruler, I realized that for me the best way to draw the scope lines is just to do two lines, one for the assumption and one directly underneath it. Then, once you're completely done with the subproof, extend the lines all the way to where your subproof ends. The ruler I designed is made to do exactly this. The space above and below the horizontal line is pretty much exactly one line at the top and bottom. This means you get just enough to start the proof without having to decide how long the lines should be. Plus, after you're done with the subproof, the edges of the ruler work just like any other and can extend the lines however far you want. I also added a lip to the end because when I was using a standard geometric ruler to draw these things, I found it extremely hard to pick up over and over again. The lip at the edge makes it much simpler to lift it off the table.