question about 10-20 map

 I am not sure about where to place electrodes. Do you pick any two
positions for each measurement are there preferred electrode locations for
certain measurements? Would it be beneficial to put one electrode where you
want to measure and try different locations for the second? From what I
understand I am trying to measure the polarity of the cells so this would
mean I want to measure across the target location. This could mean
vertically or horizontally too though.


Bonus question.

What are some interesting electrode position measurements for a beginner?

Thanks

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