The JUM Engineering Model 109A uses two individual detectors and two individual signal amplifiers. Sample is introduced into one FID for THC reading. The same sample is also run through a non-methane cutter which eliminates all hydrocarbons except methane. This sample is run through FID #2. The analyzer subtracts the two numbers to give you a THC less methane reading. This item is also available for rent from CleanAir Europe.