"INTRODUCTION The development and introduction of a full - flow@ light-extinction smokemeter by the U.S. Public Health Service (PHS) in 1968@ and the subsequent requirement for the use of this type of smokemeter in Federal smoke emissions testing@ created a demand for commercial sources of similar instruments. Experience with the PHS smokemeter demonstrated the value of this type of instrument for purposes other than certification testing@ such as engine development@ production testing@ engine maintenance checks@ and surveillance testing and also added to the demand for commercial instruments. Potential smokemeter users wanted complete instrument systems (including power supply and output devices@ backed by normal commercial distribution @ parts and warranty services) lighter @ more compact@ and more rugged@ but at least equal in performance (accuracy@ linearity @ and frequency response) to the PHS smokemeter. A large number of potential suppliers responded to this demand by developing prototype smokemeters. Following a salesman's demonstration that cigar smoke blown through the light - path did@ indeed@ make the smokemeter needle move@ many concluded that a more objective way to evaluate smokemeter performance was required@ Manufacturers also were unhappy with the ""cigar smoke"" test and were interested in a test technique which could be used to define and assess smokemeter performance under realistic conditions."