Named Range "ChartMonths":

=OFFSET('Sheet1'!$F$2,0,0,1,'Sheet2'!$P$8)

Yes, your description is correct. Reference starts in Sheet1$F$2. I
don't want any row or col offset and the data is just 1 row (i.e. $F
$2:$Q$2). The value in Sheet2!$P$8 is 1 to 12 depending on how many
months I want to show.

For the chart, I use the following Series formula:
=SERIES('Sheet1'!$E$4,ChartMonths,'Sheet1'!$F$4:$Q $4,1)

This gets an "A formula in this worksheet contains one or more invalid
references..."

Thanks for any help!