This is from another Board (Evilb1 knows this site well) it's a all mopar board but there is a lot of good tech info to be found there too. A guy by the name of Monte smith posted this.....
"The .073 jet is an industry standard. Nitrous fuel enrichment is measured in lbs/per hour of fuel, not pressure. Pressure is all relative to the amount of fuel added. The reason the .073 jet is suggested, is because as I said, it is an industry standard. If you call me and say you have a (insert jet number here) flowing at 6lbs, through a .073 jet, I know roughly the lbs/per hour of fuel you are flowing. And at 950 lbs, we also know what the nitrous jets flow roughly, so based on these two figures, you get the nitrous to fuel ratio. You should NEVER flow with the fuel jet that you are running through your plate. It will most always be DEAD RICH and this hurts parts just as bad as lean. Your flow gauge should remain a constant, that you can depend on and the one size jet, gives you that......
On the plug reading tips from Wes, the only thing I would add, is that you should NEVER see a blue line on the electrode if you are running an NGK plug. If you see heat on the strap, you have too much timing. The strap on an NGK, will take on a red/gold crusty appearance when dead on. NGK plugs are highly suggested for nitrous use. They are by far the easiest to read. Do not use AutoLites. They are indestuctible. If you burn an AutoLite plug, rest assured the piston under it is also."
Here is a link to the whole post.
http://board.moparts.org/ubbthreads...s=+Monte_Smith&topic=&Search=true#Post1873951