If Nt is unknown, then 1 to Nt is meaningless, and division by Nt is also meaningless.
I suspect you mean that Nt is defined elsewhere, perhaps in each workbook, but could be different for different workbooks.
What is Xave ? I haven't seen that mathematical expression before. Or do you mean an average of all the entries in col A?
Why do you need a macro for this? If there are explanations for the Nt and Xave above, then I'm sure the formula you have given can be worked into any cell, eg F2, even if it has to be worked on a bit.
Any new columns can be hidden of course.
But then your expression starts with D = .... What is D?
Mark
The formula is
D = [ sum from 1 to Nt( {(X - Xave)}^2 / Nt) ]^ 0.5
I need the answer to be in cell F2 and I'm trying to avoid having a new column containing the data
{(X - Xave)}^2 / Nt).
Xs are in Column A
Nt is unknown and this code will be used for different workbooks, same sheet (1) but different values of Nt.
Thanks.

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