Hi All,

I've a set of data taken from a running machine's server. What I want to do
is to track the board's serial number changes for a particular position in
the machine. When someone changes a board during troubleshooting, the
server's data is updated with the new serial number. The excel data
extracted from the server contain a column where the "Board Serial Numbers"
are listed, the "Date", "Start Time" and the "End Time" when the machine is
used for production. With these four columns provided, I can track the
board's "mean time between failure" by subtracting the time when the board
was replaced by the initial time when the board was first utilized. For
example


ColumnA ColumnB ColumnC
ColumnD
ab123456a June 1, 2008 8:00
16:00
ab123456a June 1, 2008 16:00
00:00
ab123456a June 1, 2008 00:00
08:00
ab123456a June 2, 2008 10:00
12:00
cd567890b June 2, 2008 14:00
18:00
cd567890b June 2, 2008 ....
ef987654c June 2, 2008 ...
ef987654c June 3, 2008 06:00
10:00

Initially, I have this serial number (ab123456a) on June 1, 2008 @ 8:00 when
the machine have started running production, but assuming the board was
replaced on June 2 @ 14:00, the serial number was also changed to cd567890b,
and so on..
How do I create a worksheet function such that when it detects a change in
serial number, it will subtract the time when it was changed by the initial
time when the machine have started running, and do the same thing when it
detects another change in serial number? Is this possible?? PLease help.
Thanks. :-)