In 2015 all of the publishers contracts were up for renewal and they decided they wanted more control over the price of e-books. (goodereader.com)
A stop limit order lists two prices and is an attempt to gain more control over the price at which your stop is filled. (cannontrading.com)
Using a market order provides the best opportunity to have an order filled, but it gives less control over the price at which the order gets filled. (td.com)