I discovered this tutorial about rotary cutting that uses a big square ruler. I LOVE it! Even though I have a GO strip cutter, this is the method I prefer using my 15.5" ruler. Fast and accurate. It has turned my 12.5 and 15.5 rulers into essential tools for cutting as well as use in squaring up, etc. I have smaller square rulers but seldom use them anymore.
Here's the tute:
https://www.youtube.com/watch?v=NoBKOv3Azzw