On 17 October 1987, the Dow dropped 508 points, a 22.6% loss in one day. Part of the loss was triggered by ‘programmed trades’ (the forerunner of algorithmic trading): when a share falls to a certain level, it activates a sell order in that share, to protect the investor against further falls. This process turned out to be ‘self-feeding’, because as the market fell, more shares were sold, which in turn triggered further selling orders. As a result of this, trading now stops for a specified time if the market falls 10 to 20%, and for the rest of the day if the fall is as much as 30%, in order for the market to evaluate the position.