Pen Holder for Deltahub Re-usable To-Do List

This is the small round pen-holder in the image above, connected to a Delta Hub / DeltaHub 2-card todo list (not included). The white ones are prototypes, but gives a better idea of what the black thing disappearing into the contrast actually is. The pen holder goes between the two rails and over the edge of the todo list holder, and holds their really specific thin markers. Why would you use this, instead of laying the marker down in the tray? The ink seems to flow better if it rests tip-down, rather than on its side. Really, that's it. Would you need this if you don't have a Delta Hub todo list? No. It's really specific to that thing. You're welcome to remix, modify, etc this. It would be easy to modify the opening to fit pretty much anything you'd want to hold on the edge of this very specific thing.