4.5. The Order Counter
An order counter can be enabled if the OrderCounter directive is set to a file name. An incrementing count of all orders will be kept and assigned as orders are placed. By default, the number starts at 0, but you can edit the file and change the default starting number at any time.
This capability is made possible by the File::CounterFile module, available (as a part of the fine libwww modules) at the same place you got Interchange. It is included with the distribution.