[Boatanchors] Calibrating S-Meters & Marconi Attenuator

[W8KZW]

I am certain I am revisiting a subject that has already been addressed here,
but to avoid combing through months and months of threads, I'll ask for some
bandwidth...

I have read that "the proper way to set up the S-meter would be to use a
signal generator set to 500uV and a 20 dB inline 50 Ohm attenuator".

My question is, is the 500uV peak-to-peak, peak, or RMS?

Also, I have picked up a wonderful Marconi attenuator, with both input and
output labeled "75 Ohm".  At frequencies ranging from audio through 30 Mhz,
can I use it with a signal generator and HF receiver, both of which are 50
ohm devices, without too much of an impedance mismatch bump that would
render readings worthless?

Finally, should I consider an impedance matching network for the front of
the attenuator and another  for behind it?  Any ideas on what that circuit
would look like?

Thanks in advance for the help.

Jeff
W8KZW