Hi RK,
Your formula:
vlookup(A4,Sheet1!A1:T100,16,0)
Cell A4 on the active sheet contains the data that you want to find in the
table Sheet1!A1:T100. Changing Cell A4 has nothing to do with what column is
used in the table.
As it stands now, VLOOKUP tries to match the data in A4, to a cell in Column
A on Sheet 1, and then returns the data in Column P (16th column).
If you want VLOOKUP to match its data from Column E of the table, and still
return the data in Cloumn P, then you need:
VLOOKUP(A4,Sheet1!E1:T100,12,0)

Hope I have understood what you want.
Regaeds - Dave.