Not that anyone is still reading this… but I just “built” one of these. If I like it, I’ll go with the custom paper idea. So far I’ve made a few slight changes. 1) Graph paper cards instead of standard ruled or blank cards. Lines both ways and provide a handy grid for any diagrams one might wish to throw down. 2) A larger clip. You loose a little bit more space using a large clip, but one can then pop a rubber band on to the clips in the up position and attach a Space Pen right to the top. I’ve got mine just to the right at the top like the one in your pic. This way, if you slide the pen in from the right, you can pull the pen out and the clip on the pen hits the paper clip which holds the cap in place. I know that sounds odd… but it’s quite handy. It means you can pop the pen in and out without any fuss. I find it handy. I also intend to use more cards, so the bigger clip is nice. Now all I need is a nice thick piece of cardboard at 3x5 for a nice divider/backing. Which would be change 3… just hasn’t happened yet.