Re: PUlse Question.
I suppose there are two kinds. The fuel pump is driven by alternating positive and negative crankcase pressure pulses and the tachometer senses positive and negative voltage pulses from the alternator. Both are graphed as sine waves and their peaks and valleys have a measurable frequency. In the case of the fuel pump, increased frequency drives the pump faster to keep up with the demand. In a tachometer, increased frequency moves the needle to higher numbers.
Come to think of it, there's a third. Power packs are sometimes referred to as pulse packs, and there is such a thing as a pulser coil. In each case, alternating positive/negative magnetic fields are sensed as magnets in the flywheel spin around and that's used to trigger the spark in the cylinders.
Judging by your question, I'm betting you're referring to the tachometer. Marine tachometers have multiple settings for different numbers of pulses. That's determined by the number of coils in the alternator. Each coil represents two pulses, one positive and one negative. So if there are ten coils in the stator dedicated to charging the battery, it produces twenty pulses per revolution.
