Trem Face Question GEOFEX schem.....R.G.?

[markm]

This was mentioned in another topic but, I thought I'd start this thread in hopes of finding the correct answer.
In the schematic for the Trem Face on R.G.'s site, there are a number of references to V- rather than ground.
What is the difference between V- and Ground.....does it have to do with Voltage Swing of the circuit perhaps?
See the schem here; http://www.geofex.com/Article_Folders/trem_face/tremface.htm
Maybe to keep the circuit cleaner and not distort? 

[R.G.]

That is because the Trem-face is a positive ground pedal. V- is the power supply, and it's -9V.

[markm]

That is because the Trem-face is a positive ground pedal. V- is the power supply, and it's -9V.

Ahhhh. 
Many Thanks!