The upper unit fires once per rev as the crank angle sensor
runs at half e-shaft speed I think. Lynn can probably confirm
or deny. The lower unit tells the computer when to fire
the plugs and provides a handy tach signal.
We need the green wire to give us a sync signal for our data acq.

BTW this upcoming p-port wave form test is going to give use
a million times more data than has been previously available on this
subject. I am not exaggerating. Only Mazda may have more info
on this subject. In just a few minutes, while the engine revs
from 1800 RPM to 6,600 RPM, tons of data will be recorded. 3 data
points every 1/1000 of a second.  We can see exactly what the p-port
runners are doing as far as pressure waves are concerned in a mere
instant of time.

Paul Lamar