...telling me? turbo speed? manifold pressure?. when its in the white part of the scale is it spinning faster?...
basically, i guess, what kind of sensor does it use? pressure? rpm? temp? other? all of the above?
tia,
flaps

When you look at the needle with the car off that shows Neutral pressure.
When you start the car at idle the needle shows the amount vacuum. The farther to the left the higher the vacuum. Now when you go into boost (when the needle moves past the position that it was when the car was off) the needle moves to the right. The farther right the higher the boost level. It reads manifold air pressure. Factory setting is 7.5 psi max boost but in most cases the factory setting is set low around 5.5 to 6.0 psi.

to confuse the issue there are at least two color schemes for the boost guage.
Mine is yellow and white divided at 0, but some have red as well.