The rule could be anything, as funny or as serious as you want. The universe will progress in a similar way that it has up until this point, unless your changed rule prevented it from doing so.
Some examples might be:
- The invention of currency is not allowed.
- Iron is slightly less stable.
- The Ancient Greeks are able to cultivate Silphium, which does not go extinct now.
Heck yeah, I’ll try my best!
So on a euclidian chess board, moving your king one space left would be 1 space, one space up would be 1 space, and one space diagonally would be √2 spaces (some simple trig gets us there).
Chess however, does not obey the laws of Euclidian geometry nor does its physical representation show us things to scale. A king’s move diagonally is the same amount of space as a move side to side, 1 space.
It’s silly, because spaces weren’t directly supposed to represent distance or anything, but it’s funny that it works out this way
This is a problem I’ve always had with Square grids in D&D and it never occured to me that from character perspective a character is warping space to move slightly further for the same amount of movement.
Also non Euclidian! Hexagons (the bestagons) also tesselate and fix that problem nicely