Found this info here on the rating system.
Oleoresin Capsicum is the product created by a process in which ground dried Chile peppers are rendered to release capsaicin, the natural pepper resin into corn oil. Hence the name oleoresin capsicum. Capsicum is the botanical name for Chile peppers. The "Hotness"of the OC is based on the capsaicin content of the oleoresin, basically the active ingredient of the OC. The method of measure called a Scoville Heat Unit that is used to measure how hot a natural chile pepper is also applied to OC.
For example, a bell pepper has an SHU (Scoville Heat Unit) rating of zero while Jalapeno peppers rate approximately 5,000 SHU. SHU ratings of OC are based on capsaicin content.
Pure Capsaicin is a tremendous 15 million SHU. The OC used in Aerko products is 2 million SHU which contains thirteen percent capsaicin. Further, one million SHU OC is about 7 percent capsaicin and 500,000 SHU OC is approximately 3 percent capsaicin. Other OC products on the market today reportedly contain an OC with a rating of 16 thousand SHU. This hardly seems adequate. Obviously higher percentages of this kind of active ingredient are not only needed, but demanded.
If confronted with a 10% OC formula the first question should be "10% of what?". As virtually a self regulated industry there is no governing body nationally to say what the minimum acceptable SHU standard should be.
Here is how it all relates. If a product is 5% OC, of an OC rated at 2 million SHU, its capsaicin content is .675%. Another product that is 10% OC, of an OC rated at 500,000 SHU, its capsaicin content is .3%, which is 50% less than the first product.
The bottom line is this, unlike CN or CS that are known commodities with established incapacitating doses, with OC the question "of what?" is more important than "how much?".
All Oleoresin capsicum used by Aerko International is 2 million SHU including Punch III.