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One reason is that there are differences between the smoking 

 habits of a machine and a human. The way in which a cigarette is 

 smoked is probably the most important determinant of how much tar 

 and nicotine is inhaled. Humans can compensate -- and do 

 compensate -- when smoking low yield cigarettes, by altering puff 

 volume, puff duration, inhalation frequency, depth of inhalation, 

 and the number of cigarettes smoked'S ",",", *\ ", '^ As a 

 result of these compensatory mechanisms, a low yield cigarette 

 can actually result in a relatively high intake of nicotine^'. 



Beyond the human compensatory mechanisms, several other 

 factors under manufacturers' control contribute to a lowering of 

 machine ratings. These factors include the positioning of 

 ventilation holes, how fast the cigarette paper burns, and the 

 length of the filter paper overwrap ". 



To understand how the position of ventilation holes in a 

 cigarette can confound the FTC ratings, it is important to 

 recognize that the main determinants of whether a cigarette has a 

 high or low yield in machine testing are the cigarette's 

 ventilation and burning characteristics". Most low yield 

 cigarettes achieve their low ratings because of filter 

 characteristics and also because the smoke is diluted with air. 

 The air dilution is accomplished in part by placing ventilation 

 holes in the filter. What scientists have demonstrated is that 

 "although smoking machines which measure tar and nicotine do not 

 occlude the perforations," 32-69 percent of low tar smokers have 

 blocked the holes with their fingers or lips, resulting in larger 



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