$grid->get_line(257)->get_station('257_5')->Elevation;

##</code><code>##

$grid->{ 257 }{ 257_5 }[ Elevation ];

##</code><code>##

$grid->get_line($lineID)->get_station($stationID)->Elevation;

##</code><code>##

$grid->{ $lineId }{ $stationID }[ Elevation ];

##</code><code>##

my $seismic = Seismic->new( 'seismic.dat' );

for my $lineID ( keys %{ $seismic } ) {

    for my $stn ( values %{ $seismic->{ $lineID } } ) {

        $stn->[ Easting   ] -= $stn->[ Easting  ] * 0.00001;
        $stn->[ Northing  ] -= $stn->[ Northing ] * 0.000002;
        $stn->[ Elevation ] += 1;
        
        $stn->[ Other ] = int(
            ( $stn->[ Easting   ]
            * $stn->[ Northing  ]
            * $stn->[ Elevation ]
            ) / 3.0
        );
    }
}

##</code><code>##

## You didn't provide a constructor from a file
## But you could have.
my $grid = Seismic::Grid->new( 'seismic.dat' );

for my $line_id ( $grid->line_ids ) {
    my $line = $grid->get_line( $line_id );
     
    for my $stn_id ( $line->station_ids } ) {
        my $station = $line->get_station($station_id);
        
        $station->set_Easting( 
            $station->get_Easting 
            - ( $station->get_Easting * 0.00001 ) 
        );
        $station->set_Northing( 
            $station->get_Northing 
            - ( $station->get_Northing * 0.000002 ) 
        );
        $station->set_Elevation( 
            $station->get_Elevation() - 1
        );

        ## You didn't provide this attribute, presumably 
        ## cos like me you didn't know what is was        
        ## but you could have
        $station->set_Other(
            int(
                ( $station->get_Easting()
                * $station->get_Northing()
                * $station->get_Elevation()
            ) / 3.0
        );
    }
}

##</code><code>##

package Seismic;
use Exporter;

use constant {
    Easting     => 0,
    Northing    => 1,
    Other       => 2,
    Elevation   => 3
};

our @ISA = qw[ Exporter ];
our @EXPORT = qw[ Easting Northing Other Elevation ];

sub new {
    my( $class, $filename ) = @_;
    my %lines;
    open my $in, '<', $filename or die "$filename : $!";
    while( <$in> ) {
        my( $line, $stn, $x, $y, $other, $z ) =
            unpack 'A8xA8xA8xA8xxA15xa4', $_;

        $lines{ $line }{ $stn } = [ $x,$y, $other, $z ];
    }
    close $in;
    return bless \%lines, $class;
}

1;