Auto Action trigger on value change

I've seen it referenced but cannot figure out how to reference an initial value easily. I've seen examples where a "var1..." and "var3..." were used as initial and new values but unclear on how it was either set or known that these were the values of interest.

I can do it, but I created query fields to hold initial values. I don't think this is necessary, is it?

What I want to do is fire an Auto Action when a user saves a change to a particular field in their profile.

With more digging found appropriate tutorial, and reviewed source
www.joomlapolis.com/support/tutorials/120-api-usage/18358-using-cb-triggers

Still have a question, brain just not wrapping... Let me explain what I believe and ask a clarifying question.

One
$_PLUGINS->trigger( 'onBeforeUpdateUser', array( &$user, &$user, &$oldUserComplete ) )

1. This is triggered in the Back-End
2. The first $user is var1_, it is also what gets returned as "Automatic" for AutoAction and is object being updated
3. The second $user is var2_ is user doing update if not updating your own profile
4. $oldUserComplete is var3_ and it is the original data for the user object being changed

Two
$_PLUGINS->trigger( 'onBeforeUserUpdate', array( &$user, &$user, &$oldUserComplete, &$oldUserComplete ) )

1. This is triggered from Front-End
2. Question - Assuming I am correct so far, what is the second $oldUserComplete?

I think I'm close, just missig a little bit here I think...

Use the after profile update trigger and compare var1 to var3. Var 1 being the new user object and Var 3 being the old user object. Example as follows.

[var1_cb_myfield] Not Equal To [var3_cb_myfield]

The above would check if the cb_myfield field value has changed.