The percentage price

The stock action of Questcor Pharmaceuticals (QCOR) in the past two sessions offers a clinic to IBD readers wondering how they should invest during a notoriously volatile time.
On Wednesday, Questcor moved like a bungee cord. It opened sharply up in the opening minutes, then dove as much as 9% below the prior session's close of 41.66.
The percentage price swing from the intraday high of 42.80 to its intraday low of 38 was 12.6%. The stock finished the day down nearly 3%.

Add Thursday's 7% rebound in heavy volume, and you've got a two-day trading range of as much as 16%.

If anything else, Questcor teaches investors the importance of buying correctly.
Trying to enter a stock too early — ahead of the breakout from a complete base pattern — can lead to whiplash in the form of an instant 8% loss or even more.
What caused the violent trading action? Earnings news, of course.
After the market close on Tuesday, the maker of H.P. Acthar Gel (or known as simply Acthar) reported outstanding first-quarter results. Earnings per share excluding items rocketed 205% to 61 cents a share. That marked the fifth straight quarter of EPS growth exceeding 40%.
Sales leapt 161% to $96 million. Not only was that a quarterly record, but it extended Questcor's streak of accelerating top-line growth to five quarters.
After-tax margin rose to 42.3% vs. 34.7% in the year-ago period.
Officials noted in a news release that its quarterly results can be volatile. Why? The timing of orders can be unpredictable.
On the last day of Q1, Questcor says it filled an order for 180 vials, a significant chunk of the 4,111 total vials shipped during the quarter. Questcor noted this order alone added 4 cents per share to the bottom line.