Modal logic ruler

thingiverse

**This is made for use with a normal pencil** and works great with one. I've tried it with a mechanical pencil and it worked fine-ish but the spaces were a little too wide. It doesn't work at all with a ballpoint pen, at least in my experience. --- # Background A very minimal ruler I made for my modal logic class. It can either make a modal double scope line for possibility elimination and modal impl intro. Or you can just use the box and first line for a quick nec intro. Finally the single vertical and horizontal line by themselves can make 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 take quite a lot of movements to draw it right, first you have to move the ruler a little away, but not too far away from the first line, 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 quick way! Another minor annoyance when using a normal ruler is deciding how long you want your lines to be. After doing a couple of proofs with a normal ruler, I realised that - for me - the best way to draw the scope lines is just to do one two lines, one for the assumption and one directly underneath it. Then, once you're completely done with the subproof extended 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 :p I also added a lip to the end because when I was just using a normal 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.