Quote from osorico:
An increase in quantity... Note the absence of a decrease in quantity. This is where games are played while maintaining pole position. Have you ever watched volumes on DOM? Pulled quantity, in increments of 1, maintain pole position. Just one of likely many exploits, within the "rules" of the algo.

Quote from Brucelee:
This is how it works:
First-In, First-Out (FIFO) Algorithm
FIFO uses price and time as the only criteria for filling an order. In this algorithm, all orders at the same price level are filled according to time priority. It is important to note that a user loses their order priority when the order is changed in any of the following ways:
* An increase in quantity;
* A change in price; and,
* A change in account number.