Hi - I have been over at the FE forum for years,  finally arriving here...
I have been using the Pertronx stuff since the 80's when they were still Per-Lux, and am pretty familiar with them.
To add a bit to Royces post, the plastic sleeve that fits over the OEM points cam has individual magnets in it and is a significantly larger diameter than the cam itself giving wider spacing between signals. The points cam is accually a very accurate fixture for this part.
(The magnets used to be secured into the plastic ring with a band of tape and at something north of 6000 rpms they would occasionally fly out of there - it was a pita to orient them them north and south to repair it - LOL. They are one piece molded these days.)
The pick-up simply senses the magnet going by (Hall effect). I have found them to be very accurate and reliable. It is most important to ground the pick-up assembly to the distrubutor housing using the same basic ground wire as the original points used.  A bad ground here will cause, among other things, an erratic timing signal and make a tach appear to be bonkers.

(I like the spell check feature)
Jake