If you're getting weird tach readings, it can be your spark coil breaking
down at higher rpms.
I use a 22 year old Super Sun III and it seems to be accurate.

Stan Wilder

On Thu, 17 Oct 2002 10:27:28 -0600 westydriver
<westydriver@TACTICAL-BUS.INFO> writes:
> one time when chasing a really screwing problem i had my OScope (a
> rather old one)  out and plugged it in with both traces to compare
> some
> delays.  you can get the ignition pulse by just laying a lead next
> to
> one of the ignition wires.  for tach it doesnt really matter which
> one.
>   then use the normal dividing and multiplying of pulses  per
> centimeter
>   of screen at time displayed.  but i have never seen a tach that
> was
> off by very much one way or another that wasnt within the range of
> deviation.  even digital tachs have to report by sampling.   a lab
> grade tach would be far to expensive.
> jimt
> On Wednesday, Oct 16, 2002, at 23:24 America/Denver, Leon Korkin
> wrote:
>
> > Volks,
> > I know there was some talk re signal to tach in the past.
> > Would like to get or make tach checking device just to
> > quickly test tach at a set value. Anybody knows what would this
> signal
> > be? Square vaweform? Frequency?
> > TIA
> > Leon
> > 85 Subwagen Westy
> >
>
>

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