Every second could be tricky. You could try stopping calculations/
screen updating while you update the values in Excel, then recalculate
after all the values are populated for that observation.
Application.

Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
....do the updates here...
Application.Calculation = xlCalculationAutomatic
Application.ScreenUpdating = True

I'm also thinking that you might be better off updating the range via
code or actually updating the chart series references rather than
using an offset with a named range. The dynamic named range is fancy,
but it might be faster to allow the code to "hard code" the series
reference after each update.