#!/usr/bin/perl -w
use strict;
use Time::Local;
use Data::Dumper;

my @data;
my @graph;
my $one_day = 60*60*24;    #one day in seconds

while (<DATA>)
{
   next if /^\s*$/;                #skip blank lines
   my ($date, $weight) = split;
   my $epoch = epoch($date);
   push (@data, [$epoch, $weight]);
}

# input data is sorted already sorted
# But the algortihm depends upon sorted date information
# so I did that to make sure
#
  @data = sort{$a->[0] <=> $b->[0]} @data; 
                                          
# axis x will be adjusted to #days from the date of first data
# axis y is in weight  

my ($x_base_epoch, $y1) = @{shift(@data)};
my $x1_day =0;
                                            
foreach my $r_xy(@data)
{
   my ($x2, $y2) = @$r_xy;
   $x2 -= $x_base_epoch;
   my $x2_day = int($x2/$one_day);
     
   # slope is delta weight/ delta days
     my $slope = ($y2-$y1)/($x2_day-$x1_day); 
   
   # fill in missing data points...
   # by linear interpolation 
   
   for (; $x1_day< $x2_day; $x1_day++) # x interval not tested for
                                       # other than 1
   {
      my $y = $slope*($x1_day-$x2_day) + $y2;
      push @graph, [$x1_day,$y];
   }   
         
   $y1= $y2;
}

#fix-up for last data point
my ($fx,$fy) = @{$data[-1]};
push @graph, [($fx-$x_base_epoch)/$one_day, $fy];

### data to graph is in @graph  ###
### I leave that part to the OP ###
print "$_->[0] $_->[1]\n" foreach @graph;

sub epoch
{
   my $date = shift;
   my ($month, $day, $year) = split(m|/|,$date);
   my $time = timelocal(0,0,0, $day, $month-1, $year-1900); 
   return $time;
}

=prints
0 334
1 333.527659574468
2 333.055319148936
3 332.582978723404
4 332.110638297872
.....
74 298.95
75 298.6
76 298.32
77 298.04
78 297.76
79 297.48
80 297.2
81 295.4
82 293.6
=cut

__DATA__
6/26/2010 334
8/12/2010 311.8
8/19/2010 308.4
9/5/2010 300.0
9/9/2010 298.6
9/14/2010 297.2
9/16/2010 293.6