There are plenty of articles on combustion testing, equipment adjustments, and efficiency, but few on basic combustion knowledge or understanding. To some people, promoting setting gas pressure, clocking meters (natural gas only), and checking delta T provides for the best furnace safety and performance. It seems that using combustion analyzers to set up equipment; measure oxygen (O2), CO, and flue temperature; and then evaluate equipment performance and safety should be the 21st century method to test and adjust combustion devices.
Whatever our comfort zone may be, if we do not have some understanding of the combustion process and heat transfer, neither method has much meaning or value.