Freshly imported from Ninja.
>> Increases the chances of a Pokémon producing an egg.
>Not good enough, huh? :P
God, dis was difficult. This is a valid answer so far, and I cannot find anything anywhere else saying otherwise.
The chances are changed every 256 steps.
>After looking into the code with some tools of mine(calculation tools, editing tools, viewing tools, coding tools, etc.) (legality questionable?), I found some stuff on the Oval Charm. So, I ran calcs, and got a 10% increase the first time. After retrying it, it went to 11.25% increase. Tried it again. 5.75% increase, and other various numbers.