docs: def to_iris_syscal(self, filename):
          """Export to IRIS Instrument configuration file
  
          Parameters
          ----------
          filename : string
              Path to output filename
          """
          with open(filename, 'w') as fid:
              # fprintf(fod, '#\t X\t Y\t Z\n');
              fid.write('#\t X\t Y\t Z\n')
              # fprintf(fod, '%d\t %.1f\t %d\t %d\n', D');
              # loop over electrodes and assign increasing x-positions
              # TODO: use proper electrode positions, if available
              for nr in range(0, self.configs.max()):
                  fid.write('{}   {}  0   0\n'.format(nr + 1, nr))
  
              # fprintf(fod, '#\t A\t B\t M\t N\n');
              fid.write('#\t A\t B\t M\t N\n')
  
              # fprintf(fod, '%d\t %d\t %d\t %d\t %d\n', C');
              for nr, config in enumerate(self.configs):
                  fid.write('{}  {}  {}  {}  {}\n'.format(nr + 1, *config))