def store_margin_common(record, length, margin)  # :nodoc:
    header  = [record, length].pack('vv')
    data    = [margin].pack('d')

    data.reverse! if @byte_order

    prepend(header, data)
  end
def store_margin_common(record, length, margin)  # :nodoc:
    header  = [record, length].pack('vv')
    data    = [margin].pack('d')

    data.reverse! if @byte_order

    prepend(header, data)
  end
record     : Record identifier
 length     : bytes to follow
 margin     : Margin in inches