Schematic Symbols

Okay, let's see if anyone can disabuse me of my ignorance on this
matter...
In the HP service manuals for their equipment they use a few different
symbols in their block diagrams I'm not familiar with. I can't post images
right now but hopefully a description will suffice.

The first one is a circle with a Greek capital sigma inside it. What's
that all about? Is it an integrator? A summing amplifier? What's the deal
here?
Next up: a circle with a greek theta over 'f' implying some sort of
division. Is that a phase to frequency comparitor?
A circle with a single cycle of sine wave inside it: oscillator?
Plane triangles with nothing inside them. Do they represent generic
amplifiers or buffers?
A circle with just a plane theta inside it. Any ideas?
A circle divided into 4 equal slices like it's got a giant 'X' inside it.
As per the previous one, but inside a square box.
A circle with a capital 'S' inside it.
A square box with two double-headed arrows inside it in a 'X' arrangement.

That just about covers it. Any assistance would be most welcome!

Your pal,

CD