Set up your third sheet with appropriate headings on row 1. These are
based on my previous posting, updated to reflect your values:

CID (A1), Organisation (B1), 04 Sales (C1), 05 Sales (D1), Movement
(E1), Rank (F1)

You will then have to list in column A the CID and in column B the
Organisation, as follows:

746688 XYX
7837 BBBBB
1160017 ABCD
etc

Then in C2 of the third sheet you need to enter this formula:

= IF(ISNA(VLOOKUP('Data 04'!A$2:C$180,1,0)),0,VLOOKUP('Data
04'!A$2:C$180,3,0)) and in D2:

= IF(ISNA(VLOOKUP(A2,'Dec 05'!A$2:C$200,1,0)),0,(VLOOKUP(A2,'Dec
05'!A$2:C$200,3,0))

The first formula assumes the data in the "Dec 04" sheet extends to row
180, and the second formula assumes the data in the "Dec 05" sheet
extends to row 200 - adjust these ranges as necessary, then copy the
formulae down.

You said in your earlier posting that you knew how to get the
"Movement" and "Rank" columns, so I leave this for you to enter in
columns E and F.

I hope this is a bit clearer now.

Pete