Good advice Walter. In addition, if this is the first time swims cat has extracted and used the GVG with spice, it's going to take a little getting used to. Be prepared for some misfires and the general learning curve. Take your time to get a feel for the tools, no need to rush.
I know your question was about dosage, but I'd like to share some things to keep in mind if that's okay...
* Make sure all of the solvent has fully evaporated from your spice. You don't want to smoke any naptha. I usually set it out in a small pyrex baking dish or bowl under a light fan. It will oxidize some (turn yellow/orange) but that doesn't hurt the spice at all and some actually prefer it.
* Check out the GVG thread on how to get the copper brillow just right.
This is Gibran2's copper mesh. I use something like the image attached. I couldn't find the original poster who came up with the idea but it's a small copper wire with copper brillow wrapped around it several times.
If you use the brillow (which is recommended) you need to soak it in acetone for a few minutes to get off any anti-rust agents. You can also vaporize these residues off but it won't keep the shiny finish if you torch it too much.
* As far as the spice and dosage go, just be sure to start small and work your way up. As Walter said, the only way to be certain about the dose size, is to weigh it. It's really recommended to check out Amazon for a milligram scale.
http://www.amazon.com/American-Weig...F8&qid=1339217266&sr=8-2&keywords=0.001+scale
You can find them on ebay as well for a little cheaper. If you go the ebay route, just make sure you get it from somewhere other than China or Hong Kong.. The shipping can take forever.
I hope this helps!
Safe journeys and welcome to the Nexus!