Margins matter. The more Jabil Circuit (NYSE: JBL) keeps of each buck it earns in revenue, the more money it has to invest in growth, fund new strategic plans, or (gasp!) distribute to shareholders. Healthy margins often separate pretenders from the best stocks in the market. That's why I check on my holdings' margins at least once a quarter. I'm looking for the absolute numbers, comparisons with sector peers and competitors, and any trend that may tell me how strong Jabil Circuit's competitive position could be.