The content rotate articles view acts as a search bait generator, inserting a combo of an article from the first cat + one from the second cat + one from the third.  It also generates a "TERMS" link that goes to pages of links to the other permutations.   These permutations, when followed, set the TERM1, TERM2, TERM3 values that can be used in the site title.   

A typical link might be:
   http://www.salt-lake-air-conditioning.com/?section=1&cid852=46_40&ceot=Park+City+Utah+furnace+heating+replacement&ceoi=14-27

Which can be read as "for articles use#852, present articles 46 and 40 as a combo. The site title is Park City Utah furnace heating replacement"

So traffic that comes in from links made by the generator preserve the permutation of that link.

If there is no link to set which article permutation to show, the "Default article to show for SEO" value when you configure the block can be used.   If it were 46_40, then the permutation shown would be articles 46 and 40 combined.

The TERMS link will contain all other permutations EXCEPT if a $ sign is used.  the value 46_$40 would be read as "ever possible article from cat 1 with article id=40 from cat2".  The $ sign locks in that particular choice and excludes other permutations of it.

The ability to specify permutations is made stronger by the ability to have multiple specifications, one per domain, each with its own defaults.

46_40,www.carwindows.com:34_56,carwindows.com:35_$65

means

• use articles 46_40 if you can find anything better to do
• If the domain is www.carwindows.com, show articles 34 and 56, and have a TERMS link with all permutations, all pointing to this domain.
• If the domain is carwindows.com, show articles 35 and 65, and have a TERMS link with all permutations that includes article 65, all pointing to this domain.

Sometimes you have a domain you no longer use, maybe something completely unrelated. You can have that domain direct traffic not to itself, but to your preferred domain.  

The specification
   mytoenails.com:$49_$55:www.carwindows.com

Means for traffic that arrives to mytoenails.com show articles 49 and 55 and show only the permutations that contains both of these (in other words, show no permutations).  However, ALSO show all permutations but direct them to www.carwindows.com.  This causes the junk domain to contian references to the preferred domain and not to itself.

Even if the domain is not a total junk domain and is related in name, you still might want to direct traffic to a single preferred domain and perhaps raise its link scores.

With many domains you can get confused as to what is directing where. A spreadsheet can help you generate the article specification.   Here is one from real life:

46_55,backcountryguiding.com:$45_$66:www.salt-lake-air-conditioning.com,www.backcountryguiding.com:$47_$54:www.salt-lake-air-conditioning.com,salt-lake-air-conditioning.com:45_56,www.salt-lake-air-conditioning.com:45_55,salt-lake-furnace-and-heating.com:45_38,www.salt-lake-furnace-and-heating.com:45_39,scs-air-conditioning-and-heating.com:$49_$55:www.salt-lake-air-conditioning.com,www.scs-air-conditioning-and-heating.com:$45_$56:www.salt-lake-air-conditioning.com,scssheetmetal.net:$45_$54:www.salt-lake-air-conditioning.com,www.scssheetmetal.net:$45_$58:www.salt-lake-air-conditioning.com

If you see one of these, break it down by commas and then review each specification.

1. 46_55,
2. backcountryguiding.com:$45_$66:www.salt-lake-air-conditioning.com,
3. www.backcountryguiding.com:$47_$54:www.salt-lake-air-conditioning.com,
4. salt-lake-air-conditioning.com:45_56,
5. www.salt-lake-air-conditioning.com:45_55,
6. salt-lake-furnace-and-heating.com:45_38,
7. www.salt-lake-furnace-and-heating.com:45_39,
8. scs-air-conditioning-and-heating.com:$49_$55:www.salt-lake-air-conditioning.com,
9. www.scs-air-conditioning-and-heating.com:$45_$56:www.salt-lake-air-conditioning.com,
10. scssheetmetal.net:$45_$54:www.salt-lake-air-conditioning.com,
11. www.scssheetmetal.net:$45_$58:www.salt-lake-air-conditioning.com