The following link is the Duct Blaster Manual, see chapter 13, it will do a better job than I will.
http://www.energyconservatory.com/download/dbmanual.pdf
Also here is a link to a study on measuring air flow where I first got the idea that I should use my Duct Blaster for this purpose.
http://efficientcomfort.net/document...AC_Systems.pdf
Personally my Duct Blaster results were not perfect, the numbers when compared to other methods I was using seemed to run about 3% high. My final numbers are actually a extrapolation using all my sources. I used the same method of calculation for all test so that it should not have much effect of the accuracy when comparing low to high stage.
If I stay motivated, my next idea for calibrating the Duct Blaster, at similar air flows, is to set up an air handler with a electric heaters and use the temp rise method to compare against.