It seems to me that it had to be more than typing a B instead of an M. As it turns out I just happened to be watching CNBC and eating lunch when all this occurred. CNBC just happened to be looking at P&G when these events apparently started. P&G was trading right around $60 when it started.

Did the trader type Buy xB @ $59 or Sell xB @ $59 when they meant xM? How could either one of those trades have accounted for PG dropping to $40?

It is notable that PG only has 2.8B shares outstanding. How could a trade, that at a minimum represented 1/3 of the shares of PG, get in the system?