from here
At the top - right under "The perfect authentic cadence. V (dominant) - I (tonic)", in second measure, they have "6 over 4 over V" on first two beats and then "7" on 3rd beat...
What happens in this measure?? Why is not there Roman numeral under 7??
In figured bass notation thirds and fifths are implicit in root position chords. Therefore, if you just see a "7", this means R, 3, 5 and 7.
It is because the 7 concerns also the dominant. You have two different chords for the same function.
I understand your question. I think this is indeed a mistake in the notation, if my music theory isn't too rusty.
The first two beats of the second measure are indeed clearly a tonic (I 6over4), considering that the notes are dbdg. And only on the third beat it becomes the dominant (be it dominant seven). The V should indeed be on the third beat under the 7.
I think the correct notation would be:
1..2..3..|1..2..3..|1..2..3..||
I..6..ii6|I64...V7.|I........||
