typeracer: NOS octane booster cannot raise the octane level to 100+ ... that would be impossible, you can only have 100% octane gas (100 octane). you cannot have more than 100% of something. However, NOS probably adds a anti-knock additive. So when 76 gas company says that "NOS only raises the octane level by .4%" they are correct, however, it could still be raising the anti-knock level so that detonation will not occur.. A very simple test to see if the stuff works would be to do the following :
1. run your car untill it is upto operating temp.
2. grab a timming light and advance the ignition untill you hear slight knocking then mark the point it's at with a marker.
3. put your timming back to stock and add the NOS additive.
4. Drive around for a little to let all the non modified fuel in the pipes to burn off and to let the additive mix with your fuel.
5. get out the timming light and start to advance the timming untill you hear knocking and then mark the spot on your distributor with a marker.
If you are able to advance your timming further with the additive, then your octane is being boosted...