The maximum true speed increase that can be obtain–ed through development is 60% to 100%. For slow and medium speed conventional films, preferred speed in–creasing developers are high acutance types such as FX 1, Acutol or Acuspecial. For all films we recommend Ilford DD-X, FX-37/39, and ascorbate-based developers such as Xtol, FX 50 and FX 55.