Thank you for Q and A.  If your own number is absolutely unique why should it confuse relationships?  Also have read that the primary key can include more than one field. Could this be the unique number and auto number?

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Reply from Richard Rost:

You CAN use your own number for an ID field. You don't HAVE to use an Autonumber, but I recommend it. If you use an Autonumber you don't have to worry about assigning unique values or dealing with changes in the value. If you want to have a 2nd number (your custom number) on the record too, that's fine - but don't use it for relationships. Again, just MY OPINION from my 20+ years of building databases.

Yes, a "key" can contain more than one field. This is called a composite key.  I cover them in one of my lessons... I forget which one though. :)