I took a really good class from a guy who's a a rep for Jonsered, which is what I had purchased prior. Part of the class was on how a chain works and therefore how to properly sharpen. After that I had stopped using the dremel type sharpener I had been using and switched to a file with the following:
[edit] not sure why this doesn't work, copied and pasted link twice, works fine in browser by itself.
http://www.husqvarna.com/us/forest/...cessories/filing-equipment/combination-gauge/
It helps with the correct angles and also includes a tool for the depth gauges. I have tried a few different things, but this is the best thing I've found.
As I mentioned before, I generally don't sharpen in the field. As suggested in the class I took, it's best to purchase three chains and a sprocket, and rotate between them. I bring the extra chains to the field and swap them out. I leave the sharpening to be done down in my basement with the vise. One of the main reasons for the grinder was the idea of doing chains without having to swap them out on the saw. The chain doesn't need to be on the saw for this rig.
One problem with the grinder is that it's designed to do all the teeth the same. I was taught to sharpen on a per-tooth basis. If one hit a rock that another didn't, they will be fild down beyond the damage more then the unaffected tooth. The key to being able to do this is the depth gauge tool as seen above. It fits from the leading edge of the tooth to the base of the next tooth, you file down the depth gauge that comes up through the slot. You don't put it across two teeth like most of them out there.