One year ago today, traders around the world were rocked when the Dow Jones Industrial Average plunged almost 1000 points at 14:47 Eastern Standard Time – only to recover most of its losses within half-an-hour.

The 20-minute freefall of US blue-chip companies was the biggest one-day point decline on an intraday basis and was believed to have been prompted, or at least exacerbated, by an over-sized order that was sent into the market mistakenly.