06' Tire Pressure Monitoring System

From the '06 Owner's Manual (p. 131):

"(l) Low Tire Pressure Warning Light
This light comes on when the “IG- ONâ€
mode is enabled. If the tire pressure
warning system works properly and tire
inflation pressure is appropriate, the light
goes off after a few seconds.
This light comes on or flashes in the following
cases when the “IG- ON†mode is
enabled.
o When the low tire inflation pressure
is detected while driving...
If any tire has low inflation pressure,
the light comes on.
The light goes off after the tire inflation
pressure is adjusted to a specified level.
o When initializing the system...
If initialization is completed, the light
blinks three times.
o When the system malfunctions...
If the system malfunctions, the light
blinks.
Although it is no problem to continue
driving, have your vehicle checked by
your Toyota dealer as soon as possible."

I have also attached a picture from the manual showing the actual icon that is displayed on the screen (hard to see, looks like a cross-section view of a deflated tire with an exclamation mark in the middle.

From the tech manual, the tire pressure is determine via individual pressure sensors in the wheel that wirelessly talk to an ECU (as opposed to the less-accurate method that uses wheel rotation measurements from the ABS, etc. system to determine a wheel may be low).

Open questions (I have not looked in the tech manuals with enough detail to see whether these are answered there):

1) What's the threshold at which a tire is considered under-inflated?
2) Is that threshold relative or absolute (in other words, if someone inflates their tires to 40-42 PSI, will the gauge come on at, say, 5% below this value, or at a set PSI, like 25-30 PSI, based on the factory tire inflation recommendations?

Note that there is a reset button for reinitialization of the tire pressure monitoring system (presumably after tires are properly inflated?). Its under the steering wheel next to the SKS cut-off switch. Presumably, this implies the answer to #2 is that the system is relative, and thus needs to know when you've reinflated all tires to the proper level. If it were absolute, then I don't understand the reason for the reset button, unless it allows you to set the appropriate tire inflation value, like if you want to inflate up to 40+ PSI on the OEMs, or if your replacement tires require a different inflation pressure.