docs: def get(self, col1, col2, method, channel_width, flow_rate=None,
              viscosity=None, add_px_err=False, px_um=None):
          """Get isoelastics
  
          Parameters
          ----------
          col1: str
              Name of the first feature of all isoelastics
              (e.g. isoel[0][:,0])
          col2: str
              Name of the second feature of all isoelastics
              (e.g. isoel[0][:,1])
          method: str
              The method used to compute the isoelastics
              (must be one of `VALID_METHODS`).
          channel_width: float
              Channel width in µm
          flow_rate: float or `None`
              Flow rate through the channel in µl/s. If set to
              `None`, the flow rate of the imported data will
              be used (only do this if you do not need the
              correct values for elastic moduli).
          viscosity: float or `None`
              Viscosity of the medium in mPa*s. If set to
              `None`, the flow rate of the imported data will
              be used (only do this if you do not need the
              correct values for elastic moduli).
          add_px_err: bool
              If True, add pixelation errors according to
              C. Herold (2017), https://arxiv.org/abs/1704.00572
          px_um: float
              Pixel size [µm], used for pixelation error computation
  
          See Also
          --------
          dclab.features.emodulus.convert: conversion in-between
              channel sizes and viscosities
          dclab.features.emodulus.corrpix_deform_delta: pixelation
              error that is applied to the deformation data
          """
          if method not in VALID_METHODS:
              validstr = ",".join(VALID_METHODS)
              raise ValueError("`method` must be one of {}!".format(validstr))
          for col in [col1, col2]:
              if col not in dfn.scalar_feature_names:
                  raise ValueError("Not a valid feature name: {}".format(col))
  
          if "isoelastics" not in self._data[method][col2][col1]:
              msg = "No isoelastics matching {}, {}, {}".format(col1, col2,
                                                                method)
              raise KeyError(msg)
  
          isoel = self._data[method][col1][col2]["isoelastics"]
          meta = self._data[method][col1][col2]["meta"]
  
          if flow_rate is None:
              flow_rate = meta[1]
  
          if viscosity is None:
              viscosity = meta[2]
  
          isoel_ret = self.convert(isoel, col1, col2,
                                   channel_width_in=meta[0],
                                   channel_width_out=channel_width,
                                   flow_rate_in=meta[1],
                                   flow_rate_out=flow_rate,
                                   viscosity_in=meta[2],
                                   viscosity_out=viscosity,
                                   inplace=False)
  
          if add_px_err:
              self.add_px_err(isoel=isoel_ret,
                              col1=col1,
                              col2=col2,
                              px_um=px_um,
                              inplace=True)
  
          return isoel_ret