On sheet 1 Column1 is a date function that returns the number of months sales
have come in, it is formatted as a number. On the same sheet in Column 2 I
want to sum the sales from another sheet ('PTD Comp Finney'!).

Sheet 1 Data
Column 1 Column 2
0 =IFERROR('PTD Comp Finney'!D16," ") - This is correct

1 =IFERROR('PTD Comp Finney'!D16," ") - If column 1=1, then I
want to calculate =IFERROR('PTD Comp Finney'!D16:D17," ")

2 =IFERROR('PTD Comp Finney'!D16," ")- If column 1=2, then I
want to calculate =IFERROR('PTD Comp Finney'!D16:D18," ")

3 =IFERROR('PTD Comp Finney'!D16," ")- If column 1=3, then I
want to calculate =IFERROR('PTD Comp Finney'!D16:D19," ")

4 =IFERROR('PTD Comp Finney'!D16," ")- If column 1=4, then I
want to calculate =IFERROR('PTD Comp Finney'!D16:D20," ")

5 =IFERROR('PTD Comp Finney'!D16," ")- If column 1=5, then I
want to calculate =IFERROR('PTD Comp Finney'!D16:D21," ")

and so on...

Any help would be most appreciated.
--
cheers,
Heather