#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11109362
use warnings;

my %suffix = qw( K 3 M 6 G 9 T 12 );

while( <DATA> )
  {
  print s/(\S+)([TGMK])\s+(\S+)([TGMK])\K/ '   ' .
    ("$1e$suffix{$2}" - "$3e$suffix{$4}") /er =~
    s/((000){1,4})$/ +{reverse %suffix}->{length $1} /er;
  }

__DATA__
324K    324K
440K    533K
23T    224G
42G    42G
1.9T    709G
294K    294K
684K    684K
492K    492K
62M    64M
48K    41M
34M    433K
317K    812K
[download]

Outputs:

324K    324K   0
440K    533K   -93K
23T    224G   22776G
42G    42G   0
1.9T    709G   1191G
294K    294K   0
684K    684K   0
492K    492K   0
62M    64M   -2M
48K    41M   -40952K
34M    433K   33567K
317K    812K   -495K
[download]