Ilford makes reference to 4 different color filter calibration standards on page 3 of this document: http://www.ilfordphoto.com/Webfiles/...0201152306.pdf. Two different standards are documented for Durst enlargers. There is a single standard from Kodak which is used on Beseler and Omega enlargers. The Leitz Focomat V35 uses yet another standard. There may be others. Use the one that most closely matches the setup of your enlarger and fine tune from there.