What are the odds of random encountering a female shiny Eevee on Route 4?

Question

Over-world encounter, factoring in all the other possible encounters and encounter rates. With and without shiny charm and no combo; both sword and shield.
Please include all weather possibilities uwu

Just wondering if hypothetically if I decided to run into the grass on route 4 and found that what the odds would be :eyes:

I’m assuming they’re astronomically low which is why I’m curious

Answer 1

Assumptions/Details

So from conformation, they have both games. This matters for the calcs actually. There is no weather that affects this, and I'm assuming that you're running in blind, as I'm not going into optic probability. I'm not calcing with combos, and I'm calcing for with and without shiny charms.

Sword

Here are the calcs:

Shield

Calcs:

Visualization

The shield one is the same, because I'm talking about ONLY eevee encounters.

Sources:

A crapton of bulbapedia and serebii, rather not list all of them.