For example, up until now, the highest flight number we could use on a normal schedule was Flight Number 3999. By starting from scratch for these three days (in addition to the standard Monday *and* Saturday optimizations), we quickly ran out of flight numbers. So we upped the flight number limit to 5999--which sounds so innocuous, but you'd be amazed how much testing we had to do with dozens of other, internal computer systems to make sure they could handle flight numbers in that range!