Hi
try the following:
Assumptions:
- sheet 1, col. a contains your date values starting in row 1
- sheet 2, col A contains the call start and col. B the call end.

Enter the following formula in cell B1 on sheet 1:
=SUMPRODUCT(--('sheet2'!$A$1:$A$1000=A1),--('sheet2!$A$1:$A$1000<A2))
this counts all calls STARTED in your 5 second range. Copy this formula
down for all rows




--
Regards
Frank Kabel
Frankfurt, Germany


Andrew wrote:
I have a worksheet which contains the time a call came in and the
time it ended. What I am trying to find out is for each one hour
period during a day (or even better, what 30 minute period), what was
the peak (maximum) number of callers at any one time and what time
(if possible, in 5 second increments), were there the most concurrent
callers.

To set this up, I have one spreadsheet with the values of the
date(38109 = 05/02/04)

formatted date date
05/02/04 12:00:35 PM 38109.500405083700
05/02/04 12:00:40 PM 38109.500462954100
05/02/04 12:00:45 PM 38109.500520824500
05/02/04 12:00:50 PM 38109.500578694800
etc. in 5 second increments

On the other worksheet I have the call records:
call_start call_end
38109.50041 38109.5024
38109.50431 38109.5048
38109.5055 38109.5125
...etc

So for this example, the peak number of callers would be 2 at
12:00:35 PM (38109.500405..)

Any strategies you can pass along would be of great help. Is this
something that I can only solve using ExcelVBA or is there an array
formula that can handle this?

Sorry for the cross-post, but just want to cover my bases with
finding a solution.

-Andrew