"CX" capacitor in Tremface schematic?

[sfr]

Looking at the Trem Face schematic on Geofex ( http://geofex.com/Article_Folders/trem_face/tremface.htm ) and I'm a bit confused - what's a good range of values for the capacitor labelled CX on the tremface schematics over at GEO?  I assume it's not crucial or it would be labelled, but anyone have an idea?  Can someone explain it's purpose so I'm a bit more certain?

[sfr]

this got bumped off the main page w/o a reply, (tends to happen with very late night posts sometimes) thought I'd bump it 'cause I'm still curious - hope I'm not being rude.  I've probably just missed something obvious in the article text, although I've read through it a few times.

[R.G.]

I never could figure out what it was or why it was there. "Cx" was my best guess; some very low value capacitor, maybe for RF pickup suppression.

The circuit works fine without it as I remember.