I'm confused by this paragraph:
Most blues harp players play in second position, that is, say, for blues in the key of G you use a C harp. Now if you are a better harp player, and you really should have this in your repertoire, you can also play blues in D on a C harp, which is called third position.
...it goes on to explain that 3rd position is the most common approach to blues on a chromatic harmonica (which has a different layout to a "blues harp" or diatonic harmonica).
I understand the basics of modes, how you can start on the second note of the scale for a Dorian etc. But why is a tone up, called "third position", and does this have any relation to positions on guitar, or is it a harmonica-specific thing...? The numbering of the "positions" on guitar always confused me too, and I'm thinking there's some basic/universal music theory here I'm just not seeing...