Hi Rainer,
turns out, org-table-sum is an old function I have not looked at for a
long time. It used (format "%g" res) to format the final result for
display - bad idea indeed, because that causes the unwanted rounding.
I have removed this, the change has just been pushed to the git repo.
I have a problem I am confident there is a solution to. I even
suspect it may be explained in the manual, but can't for the life of
me find it:
Summing up small numbers in tables isn't a problem even when they have
digits after the decimal point. For example, org-table-sum applied on
the table
