Remember that odd numbers mean the left side
of the head.  (Scroll down for some new
information, please!)

When placing the mastoid electrode, be sure
youare on the bony part, not on the neck
muscle.  You can ask the patient to bend his/her
head towards you to feel where the neck
muscle ends.
Try it on yourself - put your index and middle
finger on the bone behind the ear and bend your
neck to that side.  Slide your fingers up and
down to see what area has muscle below it,
and what are does not, and would be the ideal
location for an electrode.

Electrodes on the mastoid or earlobe are
usually attached to the negative (also called
inverting) input on the amplifier box, which
is also called the "physiologic amplifier".