Thanks guys, the really issue here is that i know the formula that minitab use, but i am not able to replicate it in excel, i know that i need the C4 factor and all the data, i have it, but the result is not the same in minitab i am doing something wrong but i dont know what. i attached one file that other guy post here i studied the format and can't get the pooled unbised standard deviation, hope someone can help.