Universal mining profit formula

[LampLight]

Hello. I've seen sites with profit calculator like whattomine, for example. And thought, how do they calculate data about each algorithm correctly? Found kind of formula which counts profit per minute/hour/etc. but however profit for few algorithms seems fine: Ethash, Equihash but for others it's not correctly at all: Myriad-Groestl. With last i am getting number which is 2 times bigger than whattomine displays. So, how do they count profitability?