Tachometer
You can drive a tachometer with any of the outputs, if you need
a positive voltage pulse you can either use the S259 which is a
push-pull chip or you can use an external pull-up resistor to
+12 V.
The calibration is done through the divider.
Boost Gauge Settings
For the Audi S2/4x (what year? models?) gauge. Known good
default settings are unknown.