Graph only last 7 cells of a given range?

Can I graph only the last 7 cells of a given range?

I graph daily stats, and the range increases automatically as I add in each new day. This is ok for graphing the TOTAL stats, but how can I make it automatically graph just the last 7 cells of the range?

When I setup a graph to graph the last 7 cells, when I add a new day, it either extends it to 8 cells or does not extend it at all which ignores the new day.

Suppose you have a dynamic named range chtData that contains x values in the left column and y values in the right.

Then define

chtLast7 Refers to =INDEX(chtData, ROWS(chtData)-6, 0):INDEX(chtData, ROWS(chtData), 0)

chtX Refers to =INDEX(chtLast7, 0, 1)

chtY Refers to =INDEX(chtLast7, 0, 2)

... and edit your series to plot chtX versus chtY