docs: def pmt_angles(self):
          """A list of PMT directions sorted by PMT channel, on DU-1, floor-1"""
          if self._pmt_angles == []:
              mask = (self.pmts.du == 1) & (self.pmts.floor == 1)
              self._pmt_angles = self.pmts.dir[mask]
          return self._pmt_angles