Set element top/bottom margin without line-height minus margin

gistfile1.sass

@function margin($margin,$lheight,$base,$unit:0){
	@if $unit != 0 {
	@return ($margin + (((1 - (($lheight) / $base)) / 2) * $base))+px;
	} @else {
	@return ($margin + (((1 - (($lheight) / $base)) / 2) * $base));
	}
}