Pertronix uses a smaller-than-need-be magnet embedded plastic wheel that serves as the trigger wheel.
Due to the small diameter and cheesy plastic wheel, errors of up to 1.5 to 2 degrees have been reported and by Pertronix themselves.
We will not see this degree of errors with Photo-Eye or VR.
Shown below is a variance of Hall Effect. This system uses a steel trigger wheel.... much like VR.
To some extent, the gap shown controls Dwell Angle.
This is an actual Pertronix Ignitor unit in Retro-Fit form.
You can see the plastic triggering wheel.
For a Retro-Fit, the wheel is placed over the Ketering System cam.
Whereas with a Pertronix distributor system, the wheel is fitted in a much better and permanent fashion.
The VR (variable reluctor) trigger wheel is not much larger in diameter, if any.
However, the reluctor wheel is a precisionally machined part, which equates to more accuracy.
The photo-eye wheel is larger in diameter and is precisionally machined, which also equates to more accuracy.
BTW, the Chrysler Motors Company pioneered VR back in the early 70s, and it has stood the test since then.
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