I've always wondered about calibrating the tachometer.
 Adjusting it based on your speedo.  But I've never trusted
my speedometer.  I don't have any mile markers in my
area to check my speedo.  I've contemplated rigging up
a temporary tach to my half-shafts to get wheel rpm.
This way I could check both speedo, and tacho.  But I
've always had other projects to consume my time!
Can somebody tell me, is the tach pulse driven or voltage
driven?  Does the W terminal issue a variable voltage,
or a frequency?  I suppose I will need to test this myself...
opps, I can't until my car gets back on the road.

snip...
The Quantum tach is calibrated
>for the pulley ratios of the Quantum alternator. It
was way off from the
>needs of the Vanagon pulley system. I anticipated this
and while I had
>the tach out of the housing I drilled a small hole in
the back of the
>housing. This hole lines up with an adjustment pot in
the tach. I can
>just reach it with a small screwdriver and change the
setting as needed.
>I used a tranny gearing chart and measured the circumference
of my
>wheels. I then calculated the engine rpm at 65 MPH in
4th and adjusted
>the pot a few times until it was right.
>
>Mark
>

-Gary, San Diego
1979 Rabbit 1.5 dsl, 180,000mi(sold)
1981 Rabbit 1.6 dsl, 150,000mi(sold)
1985 Quantum 1.6 td, 145,000mi(current)

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