my @numbers = qw /0.12 0.35 1.34/;

my $diff = -1;
my $di   =  0;


for (my $i = 1; $i < @numbers; $i ++) {
    my $d = abs ($numbers [$i] - $numbers [$i - 1]);
    if ($d > $diff) {
        $diff = $d;
        $di   = $i;
    }
}

if ($di) {
    print "The diff between $numbers[$di - 1] and $numbers[$di] is $diff.\n"
}