There has long been discussion about the credibility of the fitting loss coefficient data in the ASHRAE Fundamentals Handbook chapter on duct design. A forum was conducted 26 June 1983 at the Annual ASHRAE meeting in Washington, D.C. to discuss the source and accuracy of the data. A summary of the major comments made regarding the chapter included: (1) Some coefficient data was developed or investigated over 50 years ago. (2) The chapter has several inaccuracies and is incomplete. (3) Variations were as much as -42% to +54% for a 6-inch elbow from four different sources. Much of the loss coefficient data listed in the chapter originated from a translation of a Russian manuscript (Idel'chik, 1966). The main reason for this was the lack of other information for many of the fitting constructions. His handbook is a compilation of data checked satisfactorily by laboratory studies but also includes data obtained by crude experiments, data obtained theoretically, data obtained from approximate calculations, and other methods. Idel'chik felt that publishing all data available was justified since "the accuracy with which conduits and components are manufactured and installed under industrial conditions can differ considerably from installation to installation and also from the laboratory conditions under which most coefficients were obtained." Idel'chik warns in his FOREWORD, "it would have been better to delay the publication of this handbook until all coefficients could have been checked experimentally by some standard method..."