Knife sharpening angle blocks

For years I have wondered if I was sharpening knives at the proper angle for their use. I came across something like this on amazon a while back but couldn't justify buying them when I could just make my own. This is just my first draft of these. If you have any suggestion on what I can add let me know. I believe you are supposed to put this block at the end of your stone to get the knife angle then slide your knife along the stone keeping that angle but not dragging the block along. I printed these at a fast speed so they didn't turn out super well in the photos but they still work.

The most popular knife sharpening angles are 17-20 degree's per side. I included the 10, 12, and 15 for things such as xacto blades or razor blades. The 25 and 30 I am not sure what they could be used for. Maybe sharpening an axe or machete? Let me know if you want a specific angle and I will try and design one for you.