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;
}

##</code><code>##

#! perl -slw
use strict;
use Time::HiRes qw[ time ];
use Data::Dump qw[ pp ];
use List::Util qw[ sum ];

sub coffOfVar {
    my $mean = sum( @_ ) / @_;
    return 0 unless $mean;
    my @dif2s = map{ ( $_ - $mean )**2 } @_;
    my $stddev = sum( @dif2s ) / $#_;
    return $stddev / $mean
}

my @data;
push @data, [ map rand( 2000 )-1000, 1..7 ] for 1 .. 55*1024;

my $start = time;
my @results;
push @results, sprintf '%.5E', coffOfVar( @$_ ) for @data;

printf "Took %.2f seconds to find the coffOfVar of %d datasets\n",
    time - $start, scalar @data;

__END__
C:\test>802855.pl
Took 0.59 seconds to find the coffOfVar of 56320 datasets