docs: def inc(self):
          """Corrected inclination, taking into account backsight and clino corrections."""
          inc1 = self.get('INC', None)
          inc2 = self.get('INC2', None)
          if inc1 is None and inc2 is None:
              return None
          if inc2 is None:
              return inc1
          if inc1 is None:
              return -1 * inc2
          return (inc1 - inc2) / 2.0