CEMS and making sure they pass. How many of you know how far your analyzer can drift before it fails? 
Let's look at a simple example.

NOx analyzer with a span of 250 ppm​​​
What is desired 196 minus what you ran 220.3 = -24.3 then divide that by the span of 250 and times 100

(196-220.3)/250*100= -9.72