1.13Roman numerals versus ordinary numbers

We'll use both.

For individual notes, I will generally write:

1 2 3 4 5 6 7

For chords built on those notes, traditionally:

I ii iii IV V vi vii°

In C:

1 = C note

I = C major chord

2 = D note

ii = D minor chord

5 = G note

V = G major chord

This distinction becomes extremely useful.