docs: def convert_source_location(self, source_reading, reference_reading):
          """
          Converts the source (x, y) location from reading into the coordinate
          system of reference_reading.
          """
          offset_x, offset_y = reference_reading.get_coordinate_offset(source_reading)
          focus = source_reading.x + offset_x, source_reading.y + offset_y
          return focus