At around 2:45 p.m. ET, P&G's (
PG,
Fortune 500) stock had fallen 10% to $56, triggering a "circuit breaker." At that point, other stock exchanges were allowed to report P&G's stock price on their own, instead of getting the price from NYSE.
According to the company and NYSE, the Nasdaq stock exchange misprinted a quote of $39.37 a share, even though the stock was really trading at $56.