sub do_work {
    my @working_block = @input_data[$start .. $stop];  ## COPY 1
    my @partial_output_data;
    $, = undef;
    $\ = undef;

    my $output_line = 0;
    for (my $i = 0; $i < @working_block; $i += $files) {
        # calculates the stddev of each slice and outputs the formatted resuls
        if (max(@working_block[$i .. $i + $files - 1]) == 0) {   ## COPY 2
            $partial_output_data[$output_line] = '0.00000E+00';
        } else {
            $partial_output_data[$output_line] = 
                sprintf('%.5E', stddev(@working_block[$i .. $i + $files - 1]) /   ## COPY 3
                mean(@working_block[$i .. $i + $files - 1]));   ## COPY 4
        }
        $output_line++;
    }
    @ReturnData[$start / $files .. $stop / $files] = @partial_output_data;    ## COPY 5
    return;
}