Watch the C7 F9: Pt 2 online guitar lesson by Brad Carlton from Guitar Lab: I7 to IV7 Vamps

Example 22 shows a C7 to F9 move on the third, fourth, and fifth strings in which the middle voice is static and the first and third voices move down chromatically. These two voices that move are the guide tones but are laid out on non-adjacent strings. This is very useful because it opens up an interior voice between the guide tones.