bal --base
<<<
i 2007/03/01 23:00:00 A
o 2007/03/02 01:00:00
i 2007/03/11 23:00:00 B
o 2007/03/12 01:00:00
>>>1
               7200s  A
               7200s  B
--------------------
              14400s  
>>>2
=== 0