Single value to be shown as a horizontal line in control charts

Hi,

I am trying to plot a line chart with data available in excel column say A1:A10 [series 1].

What i need is along with this line chart i need to add another series [series 2] which is the average of the data in A1:A10. The option available with me is to add a formula in each cell in B1:B10 to get the average and the plot the chart so that both the data points are same [10 data points each]

MY question is - is there a way i can get the average in one cell [B1] and then create an array formula asking to repeat the value 10 times, so that i can add that as the Series 2

Thanks in advance for any help.

Regards,
Jith