code: @Override
    public void writeExternal(ObjectOutput out) throws IOException {
      out.writeDouble(m);
      out.writeDouble(t);
    }
docs: The object implements the writeExternal method to save its contents by
  calling the methods of DataOutput for its primitive values or calling the
  writeObject method of ObjectOutput for objects, strings, and arrays.
  
  @param out the stream to write the object to