Music Theory

2        D F A  (ii chord root position)
   4     C F A  (IV chord 2nd inversion)
      6  C E A  (vi chord 1st inversion)
_______
1  3  5  C E G  (I chord root position)
_______
7        B E G  (iii chord 2nd inversion)
   2     B D G  (V chord 1st inversion)
      4  B D F  (vii chord root position)

DFA 246
CFA 146
CEA 136

CEG 135

BEG 735
BDG 725
BDF 724

If you lay out any of the seven diatonic chords using digits to represent the notes, the I chord for example in C Maj would be 1 3 5.
If you then use a technique similar to that used to crack a 3 ring combination lock by going through a set sequence you can create a table of each of the possible chords; both ascending and descending; that the starting chord can progress to.

1) start with the 5 on the right, add one to make 6 which gives the chord 1 3 6
2) take the 3 in the middle, and add one to make 4 which now gives the chord 1 4 6
3) take the 1 on the left,  and add one to make 2 which now gives the chord 2 4 6

4) now starting with the 1 on the left, subtract 1 to give 7 which gives the chord 7 3 5
5) take the 3 in the middle, subtract one to give 2 which now gives the chord 7 2 5
6) take the 5 on the right, subtract one to give 4 which now gives the chord 7 2 4

NOTE the wraparound at 7 to account for the 7 notes CDEFGAB ie if at 7 and adding one instead of going to 8 wraparound to 1, If at 1 and subtracting one wraparound to 7

I'm still not sure if anyone is reading these scratchings but i'm still working slowly through a bunch of books and selected websites trying to learn music.
I'm busy now on chord progressions but though i can find loads of material on the subject i still find it hard grasping exactly what a chord progression is.
As with everything else in music the terms can be understandably vague as it is an art not a science, But that said there are still clearly rules which if defined would be usefull.

Anyway while trying to understand the function of a chord progression and especially the way one chord moves to another chord i started looking at chord movement in general and came up with this chart to try and put things in order.
My first impression is that it may be usefull in navigating from one chord to another or an aid to memorising chords, Either way i place it here in case it may be of use to others or as a topic of discussion.

Can i say in closing that my vague understanding of a chord progression is that it is the dynamic under the melody ie it adds pace(in terms of harmonic rhythm, fast, slow etc) and mood(in terms of a lifting or lowering of mood using appropriate ascending or descending progression).
I still lack a usefull global definition of a chord progression ie what is the ultimate purpose of a V-I or equivalent progression cadence not withstanding.