Depending on how the next trading day goes, this could be a bit more than "this happens about once quarter". From to the FT:
> Its shares fell more than 10 per cent in after-hours trading[...] The share price drop, if sustained, would wipe more than $400bn from the group’s market value, the largest single-day loss in the company’s history.
> Its shares fell more than 10 per cent in after-hours trading[...] The share price drop, if sustained, would wipe more than $400bn from the group’s market value, the largest single-day loss in the company’s history.