Excel 2013, wants to add 2nd axis series to chart, its not working ( need help)

created chart with 1 series on excel 2013, would like to add 2nd series as Power watts series to chart , when I go to selection and try to pick 2ns series, its grey out,.

have attached the file, can some one please help, I just installed 2013 excel, new to this , I was using excel 2010, 2013 has totally new screen , getting used to these option

thanks in advance