Mixed optical procedures. You will find many proprietary optical smoke measurement units including the 'nephelometer' or even the 'aethalometer' which use quite a few distinct optical procedures, like multiple wavelength of sunshine, inside just one instrument and apply an algorithm to provide a superb estimate of smoke. 1600 – https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/