I think you are confusing the parts your different variables play. Is this what you want?

        my $newno = 0;
        while (my ($number) = $sth->fetchrow_array) {
            $numbergraf++; # whatever that is
            $newno += $number;
        }
        $output .= qq~ The sum of xxx is $newno ~;
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I'm not sure what you're trying to do with substr, but it doesn't look consistent with a sum.