Monday was a day of bloodletting as NFL owners gave pink slips to coaches whose teams' playoff hopes were dashed on Sunday, if not long before that. The decisions can seem pretty cut and dried when it comes down to a team's win-loss record, like the Detroit Lions' 0-16 streak, which cost coach Rod Marinelli his job yesterday.And the Jets' loss of four of their last five games was too much disappointment for Eric Mangini's bosses to take. Wins and losses are cold, hard facts that can't be argued down. As in football, stock ratios are cold, hard numbers, usually based on data that can get fudged a bit. Using several ratios to value a stock helps to cover all your bases in case a company's earnings statements look a little too managed from quarter to quarter.