write a tutorial or profile for your system and ill be completely convinced.
That's tough. I'm no "writer." In short:
If a person seems to usually be focused on their environment in some way, they could be Sensing Primary.
If a person seems to occupy themselves with noticing things which may not be obvious, they could be Intuition Primary.
If a person seems to often rely on what they already know to make easy decisions regarding
impersonal matters, they could be Thinking Primary.
If a person seems to often make easy decisions using their emotions (such that an action is
morally wrong or right, for example), they could be Feeling Primary.
"More than the other three" is key, of course. If the Primary function is determined with confidence, apply the format again to possibly determine the Support function--Though you'll be choosing only between the two Functions of either Perceiving or Judging nature, the opposite of the Primary function, naturally.
And, of course, it should ideally be used in cooperation with whatever other effective methods you have at your disposal.
There is a great deal of information out there on the difference between introverts and extroverts, so I won't get into how to differentiate them here.