>track.dbf structure and sample records is like under

>date dateteime(8)      signal c(50)
>
>05/09/2002 14:53 PM    Start 1 M2A|M4D|M6A|M8A|M0A
>05/09/2002 14:54 PM    Start 1 M2A|M4D|M6A|M8A|M0A|M1A|M3D|M5A|M7A|M9A
>05/09/2002 14:53 PM    Start 1 M1A|M3D|M5A|M7A|M9A

Looking at the first record, I see Machine 2 started at 14:53 PM, right? So the SQL needs to look for the next record after that which has a M2D value in it, right? Does the M2A in the second record of the above example mean the Machine 2 is still running, so ignore it in the time calculation? I am a little confused as to how to do the calculation.