docs: def load_cell(fname="HL60_field.zip"):
      "Load zip file and return complex field"
      here = op.dirname(op.abspath(__file__))
      data = op.join(here, "data")
      arc = zipfile.ZipFile(op.join(data, fname))
      for f in arc.filelist:
          with arc.open(f) as fd:
              if f.filename.count("imag"):
                  imag = np.loadtxt(fd)
  
              elif f.filename.count("real"):
                  real = np.loadtxt(fd)
  
      field = real + 1j * imag
      return field