Assuming you have call data with start date/time and end date/time

(i.e. start date/time + duration), one way of doing this is to create

TWO records for every call record. One record to contain START date/

time and an indicator set to "S", and the second to contain END date/

time and an indicator set to "E".

Merge the two sets of records together and sort by date/time in

ascending sequence. If the S/E indicator is in column C, and assuming

first record is in row 2, then in column D row 2 add the formula:

=IF(C2="S",D1+1,D1-1)

and replicate this formula downwards to all other records (cell D1

should be initialised to 0). Column D should then contain the number

of simultaneous calls at any one time. You can easily determine the

maximum number (using the MAX function) AND the number of times that

this number, and every lower number, was reached (using the COUNTIF

function).

Hope this helps.

Pete