um, lemme think...

Palmer is a gentle manipulation by the chiropractor, with his hands, to realign the vertebrae.

Activator uses a little tool-thingie that sorta POPs out, and jiggles things back into place without the manual adjustments.

some doctors use several methods, whatever is best for the patient.

sometimes people are in too much pain to be pulled and twisted by hand, so the Activator tool works well for them.

and some people only hurt badly in one or two areas, so the doctor uses the Activator there, and manually adjusts elsewhere.

see, when one vertebrae or disc is injured, it puts stress on the whole spine (since it's all connected) and there can be a domino effect, leading to, say, if your lower back's out, then it pulls things out further upwards, leading to a tweaked mid-back or neck.

here, this explains it better than I ever could:

http://www.becomehealthynow.com/arti...echniques/663/

hope that helps.