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.