How do the mylot earnings increase?

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I always wondered how they count how many cents they give you for every post. I noticed soemtimes my earning increased a few cents only after I posted a lot, and after a few posts, sometimes they went up quite a lot. How do they calculate the earings for each post? And how much do you earn by posting images, too? Is there a specific amount they pay you for every post, or does it change everyday? If they change all the time, why does that happen? It's really annoying.