"Michael" wrote:
Is it possible to calculate a figure for two standard
deviations for a series of numbers? I have the
output for 1 SD, but need 2 SDs.

=2*sd

where "sd" is the std dev constant, STDEV(range),
or reference to a cell containing "sd".

Perhaps what you need is the data value associated
with 2sd. That would be:

=avg + 2*sd
=avg - 2*sd

where "avg" is the average constant, AVERAGE(range),
or reference to a cell that containing "avg".