I wanted to put in another site I use a lot to help me figure out quilt stuff,
https://www.incompetech.com/graphpaper/
No affiliation, just so much good stuff and updated periodically so if you haven't seen it lately check it out again. I've been thinking a lot about 3D and other illusions in fabric lately and just might be able to put this perspective grid to use in the near future...
https://www.incompetech.com/graphpaper/perspective/
When I was younger, I could do a lot more visualization and mental math. Nowadays I rely on calculators, websites, and do a lot of design on Electric Quilt or in my notebook, and I've been cheap and haven't bought an upgrade to my Electric Quilt and can't put it on my current system, so it's been notebook time.
I find that while I enjoy designing on computer, in some ways I'm more aware of construction issues when I'm working with paper. And sometimes, it just helps to count on my fingers or on my grids and I'm ok with that
