code: def add_measurement(self, exp_name, meas_num, spec_name=None, er_data=None, pmag_data=None):
          
          specimen = self.find_by_name(spec_name, self.specimens)
          measurement = Measurement(exp_name, meas_num, specimen, er_data)
          self.measurements.append(measurement)
          return measurement
docs: Find actual data object for specimen.
          Then create a measurement belonging to that specimen and add it to the data object