Flight Oximeter and 02 Saturation Standards

I just bought a FlightStat Fingertip Pulse Oximeter as an added measure
of safety when flying at oxygen altitudes (with oxygen, obviously).
Anyway, the device does not really come with any guidelines on threshold
levels below which you should be concerned.

1. A little background reading suggests that 93% is good; 89% seems to
be OK, but the lowest one would want to go to avoid any imapirment.
Does anyone know definitive values?

2. Does anyone have experience with Oximeters like this? What values do
you see at the higher altiutudes (non-cabin pressure aircraft...just
supplemental oxygen).

3. I read that, at least at one time, one could find places (often
military bases) where pilots could go and experience O2 deprivation in a
controled environment to learn about its effects and how better to
notice them. Does anyone know where on goes to try this out and how one
finds the nearest place to do this. Seems like a good safety exercise.