Profitability is important. It's the literal bottom line every investor needs to know -- but it isn't everything. Companies turn sales into profit in different ways. UPS stock has been hot and cold for investors over the past few years, and it's often tricky to pick which metrics matter most. For investors interested in understanding UPS's real bottom line, there's more to this megacorporation than many might imagine. Here are three numbers to put United Parcel Service's (NYSE: UPS) profit in perspective.