Freddy, Welcome to the Router Forums. We are glad to have you as a member!
There is no "absolutely correct proportion" of length to width for any of the 10- numerical characters, when you consider the possibility that there are literally hundreds of fonts available. Same goes for the 26- alphabetical characters. Different "fonts" do this in varying proportions.
Here's an easy way to determine what you need:
1. Choose a "font" that you like or prefer. Use one that you can print from your computer. Programs such as "Word", "Excel", "Word Perfect", etc. make changing fonts quite easy.
2. Printout the number seven in the font of your choice.
3. Feed your printer some graph paper and print the "7" as large as possible that will fit on your graph paper.
4. Measure your printed page's "7", and everything you need should be right there!
Let me know if this is not feasible in your situation, and I will be happy to help with this. I use several programs with font options and will be glad to make some test pages for you. I can "overlay" a graph in the pages also - so there is no need for an enlarging copy machine - but you will need a decent printer. Good luck, and simply add to this thread and I will check it periodically to verify if my making some sketches can help!
OPG3 Tweak everything!