Live by the tech stock valuation, die by the tech stock valuation expectations.

http://www.usatoday.com/story/money/ca…

The rapid fall shortly after today's start of NASDAQ trading triggered the exchange's short-sale circuit breaker, which doesn't happen often. The breaker temporarily stops the sale of borrowed shares by investors betting the price will keep falling so they can replace the borrowed shares later at a price cheaper than the sale price today.

Tesla shares opened trading on the NASDAQ exchange at $155, about where they'd been in after-hours and pre-market trading. The share price then plunged to $146.71 after the open before rebounding. It was trading at $152.25, down $24.56 or 13.89%, mid-afternoon. Before the after-market earnings report it had closed on Tuesday at $176.81.

Some think it has more downside risk to come. Tesla stock "is more properly valued at $141," industry analyst Brian Johnson at Barclays told his clients late Tuesday.