You got it James, Leedog, the term power chord is really just one of those made up guitar player terms to make us all sound cool, really they are Diads(2notes)normally played on the 6th&5th or the 5th&4th strings, to give a bigger sound, you can double one of the notes like playing the 6th string 5th fret/5th string 7th fret, add the 4th string 7th fret and you have added another A note one octave higher, just makes a bigger sound, thats the basic purpose of the power chord anyhow, a big sound with no 3rd to give it a major or minor tonality, this way one chord shape fits in both keys, does that help you or even make sense?