use strict;
use warnings;

my @list = (
	    [qw(1.000    64.103    2840.0)],
	    [qw(1.000    42.735    2840.0)],
	    [qw(1.000    32.051    2840.0)],

	    [qw(1.050    64.103    3280.0)],
	    [qw(1.050    42.735    3280.0)],
	    [qw(1.050    32.051    3280.0)],

	    [qw(1.100    64.103    3720.0)],
	    [qw(1.100    42.735    3720.0)],
	    [qw(1.100    32.051    3720.0)]
	   );


my @sorted = sort {
  $b->[1] <=> $a->[1]   # 2nd col (biggest first)
    ||
  $a->[0] <=> $b->[0]   # 1st col (lowest first)
  } @list;

foreach(@sorted) {
  print join("\t", @{$_}),"\n";
}

__END__
Output:
1.000   64.103  2840.0
1.050   64.103  3280.0
1.100   64.103  3720.0
1.000   42.735  2840.0
1.050   42.735  3280.0
1.100   42.735  3720.0
1.000   32.051  2840.0
1.050   32.051  3280.0
1.100   32.051  3720.0