POTW: Ruler Macro

I found myself last week trying to explain what a 1:1 macro lens meant. Figured it would be easier to just take a picture of a ruler.

Looking at this ruler and you can see the image is about 21.6mm wide (those are half mm marks under 4 and 5). The sensor size on a 40D is 22.2mm. But, if I have a 1:1 macro lens shouldn't the ruler measure 22.2mm as well? It should, but I'm thinking I took the picture just before the minimum focus distance. Another picture I took everything was blurry so I may have just refocused instead of moving the ruler closer. I hope to get the extension tubes at some point. Would turn this lens into a low powered microscope.

Apologies on the late update, memory card reader was giving issues. Also I braved the scary world outside and have something other than close up shots of random stuff in my house. And I moved everything over to the new server last week so hopefully you notice things being a little more zippier. Let me know if you notice anything not working as I still have some minor stuff to setup.