can be used for direct fire ignition
So basically the little cut out in the wheel allows an on off on off signal to be generated buy the Hall effect sensor.
That pulse is then used by the FI/ignition computer to time when and how long the ignition spark will be.
also used by FI systems to synchronize when to fire the fuel injectors
People that run Megasquirt FI systems, a lot of them head to the Junkyard to get Ford Trigger wheels and adapt them to whatever car they have
we have been needing something like this for years (that's available to every one not to just a select few)
HTH HTMS (hope this makes sense)