I gave my wonky 6 x 24" (more like 5.712 x 23.863") Olipfa ruler to a non-quilting buddy that needed a straight edge only ruler. She only uses the lines on her cutting mat to measure with. I didn't know about rulers being wrong either until I tried making swap blocks and not only were they not the right size but they weren't even square! Now, I only have Omnigrid rulers and I checked all of them against a Stanley tape measure for accuracy.

No you are not crazy. I still have problems with math, Failed math in school too, took me years to figure out basic accounting. Just don't tell me that a pattern has to be cut in a triangle shape or somesuch because I wont understand. Show me a picture of what you want and I can do it!
A bit of tidbit for you if I remember correctly: We got our foot and inch measurements from England and the sizes were never the same, due to the fact that the King set the measurements with his foot size and his hand size. I have many 'practice' blocks that I write down what I did and how to improve for the next time - it keeps the mind active and keeps the joy in quilting. Have a very blessed day! :D