use warnings;
use strict;
use Data::Dumper;

my @list1;
my @list2;
while (<DATA>) {
    next unless /\S/;
    @list1 = split;
    if (@list2) {
        my @diff;
        for my $i (0 .. $#list1) {
            push @diff, ($list1[$i] - $list2[$i]);
        }
        print Dumper(\@diff);
    }
    @list2 = @list1;
}

__DATA__
42.034 41.630 40.158 26.823 26.366 25.289 23.949

34.712 35.133 35.185 35.577 28.463 28.412 30.831

33.490 33.839 32.059 32.072 33.425 33.349 34.709