The terms "X-Out" and "Z-Out" are derived from cash registers whose security lock had an "X" and a "Z" position. A manager who turned his key to "X" could get a printed running total of sales dollars for the day by department, without clearing the unit's volatile memory.

For closing, another key would turn the lock around to the "Z" position, make a report of the day's totals and "zero out" the register. Any transactions after that would go onto the next day (or next shift), and the cash tray would normally be changed out. Often the register had three keys - one for a cashier to ring sales, one for a manager to run X-Outs, and one for Z-Outs which could do any of the three.