code: def _format_grndt(self, data_c):
          
          monthly_str = '{},{},{},{}'.format(
              data_c.header.metadata['soil conductivity'],
              data_c.header.metadata['soil density'],
              data_c.header.metadata['soil specific heat'],
              ','.join(['%.2f' % x for x in data_c.values]))
          return monthly_str
docs: Format monthly ground data collection into string for the EPW header.