#!/usr/bin/env perl
use 5.010; use strict; use warnings;

my @lines;
my $total = 0;
my $howmany = 0;
my $output_separator = "\t";  # your choice

while(<DATA>){
    chomp;
    my($n, $f) = (split)[0,8];
    my $fixlater;
    if ($n =~ /\A[A-Z]{2}\.[A-Z]{4}\Z/ and
            $f =~ /\A-\d\.\d{4}\Z/ ){
        $total += $f;
        $howmany++;
        $fixlater = 1;
    }
    push @lines, [$fixlater,$_];
}
my $mean = $total/$howmany;
for (@lines){
    if($_->[0]){ # fix this line
        my @f = (split ' ', $_->[1]);
        $f[8] = sprintf "%0.4f", $f[8] - $mean;
        say join $output_separator, @f;
    } else {
        say $_->[1];
    }
}

__DATA__
 MCCC processed: unknown event at: Tue, 14 Oct 2014 12:02:26 CST 
 station, mccc delay,    std,    cc coeff,  cc std,   pol   , t0_times  ,
 delay_times
 ZJ.GRAW    -0.7964    0.0051    0.9690    0.0139    0  GRAW.BHZ   301.1263 -1.8041
 ZJ.KNYN     -0.7065    0.0072    0.9760    0.0133    0  KNYN.BHZ 301.3372    -1.9249
 ZJ.LEON      0.9675    0.0072    0.9548    0.0292    0  LEON.BHZ 301.2611    -0.1749
 ZJ.RKST     -0.2061    0.0114    0.9404    0.0383    0  RKST.BHZ 301.3500    -1.4374
 ZJ.SHRD      0.4382    0.0051    0.9542    0.0351    0  SHRD.BHZ 301.7360    -1.1791
 ZJ.SPLN      0.3033    0.0051    0.9785    0.0126    0  SPLN.BHZ 301.0760    -0.6541
Mean_arrival_time:   300.1187 
No weighting of equations. 
Window:   2.23   Inset:   1.17  Shift:   0.25 
Variance: 0.00645   Coefficient: 0.96215  Sample rate:   40.000 
Taper:   0.28 
Phase: P        
PDE    2013  7 15 14  6 58.00   -60.867   -25.143   31.0  0.0  7.3