Whether the stock bounces from the 16-month low it hit Wednesday or sinks even lower may depend less on iPhone or iPad sales than on its guidance for the June quarter (more on that later) and what it reports about a relatively obscure ratio closely watched by analysts: the company’s gross margin, or GM%.

As always, Dewitt is keeping an eye on analyst’s estimates for the quarter to see how close to (or far off) the mark they are.