[flycaliguy]

I can report a similar visual. Mine isn't wavy, it's straight line from bottom left to top right in which each unit has a sort of notch division.

Aaaaand having to actually explain it seems to have completely messed the whole visual up. At this point I feel like I'm inventing a system based on childhood memories...

It does stretch back to my childhood though. I have strong memories of visualizing numbers in class, even specific problems like when we were asked to add all the numbers from 1 to 100. A problem in which I mentally drew half circles from 99 to 1, 98 to 2 and so on. I solved it almost instantly and thinking back I'm a little disappointed my teacher didn't investigate this more and help me explore this skill.