Envelopes are still an essential tool to cover crucial papers. Yes, also, papers are still a vital tool for record essential information.
No matter how tech goes further and spreads all around the world, somethings still using by people.
Just because no matter how fast technology developed, people's habit changes slowly. Such a measurement of modernism can not scale with tech-related improvement. Patterns of humankind are the key.
I mention the a9 envelope size above.
If you are planning to build your craft, you can apply for those numbers without any hesitation.
Here are some tutorials I found on the internet. It might help you to build your envelope. As you can see, I'm still assuming that you are looking for this number to make it.
Assuming is the foolishly think in the universe. But it can be a productive time to time. Anyway, it is a habit I can quit for now.
Have a beautiful day.