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
>