d1_square and d2_square are the combined mean deviation .
$ d1_square = ( $ mean1 - $ combinedMean ) * ( $ mean1 - $ combinedMean ) ; $ d2_square = ( $ mean2 - $ combinedMean ) * ( $ mean2 - $ combinedMean ) ; echo ( " d1 square : " ▁ . ▁ round ( $ d1 _ square , ▁ 2 ) ▁ . ▁ " " STRNEWLINE . ▁ " d2_square : "