If I understand your question correctly:

use strict;
use warnings;

use List::MoreUtils qw<pairwise>;


my @previous;
my $i =0;
LINE:while (<DATA>)
{
    $i++;
    
    my $line = $_;
    my @current = split ' ', $line;
    my @diff;
    if($i ==1)
    {
        @previous = split ' ', $line; 
        next LINE;        
    }
    else
    {
        @diff  = pairwise { $b - $a } @previous, @current;
    }
    @previous = split ' ', $line; 
    print join(" ", @diff);
    print "\n";
}
__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
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