I have a set of data time/temperature data with two temperature values
specified at each time point. I am interested in finding the time
point where the difference between this two temperatures reaches a
maximum. For example:

time T1 T2 Delta
0 175 200 25
1 150 200 50
2 100 300 200
3 175 225 50

'time', 'T1', and 'T2' are numerical values while 'Delta' is a formula
calculating the difference between 'T1' and 'T2'.

I would like to develop a lookup function to identify the value of 200
as a maximum and return the time value 2 where this maximum is
reached.

I've tried to use the MAX() as a lookup value in a VLOOKUP() function
but it doesn't seem to work.

Any ideas?

Thanks,
Russ D.