> I can guess.  The engine speed does indeed vary during a single
> revolution as you say.  However, for any particular speed and load, this
> variance is going to be predictable.  A simple mapped and interpolated
> system should therefore be adequate as these artefacts will be removed
> during the initial calibration.  For an engine in a relatively low state
> of tune an error of a degree or so is unlikely to have a noticeable
> affect on performance anyway.

I do not know if it is so easy. One degree out of 360 is 1/360 or ~0.3%.
Maybe the fact that the sensor is very close to TDC helps. When I had to
deal with this (tuned engine) 1% firing angle error resulted in vigorous
detonation. We used two sensors. After a lot of work it worked well.

Peter

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