The main page for calculating COI and viewing the details of the calculation is called Pedigree Analysis. You can access it at https://www.blackbellysheep.org/db/members/analyze.php
This article describes how to use each of the three sections of the form to analyze either
- an animal from the database
- a hypothetical mating of two animals from the database
- a hypothetical mating of the progeny of two sets of grandparents from the database.
The form expects the animal ID # for each animal.
Example 1: Dam mated to her son (sire ID #0010, dam ID #X0008)
Here’s the direct url:
https://www.blackbellysheep.org/db/members/analyze.php?said=0010&submitSDAID=Go&daid=X0008
After submitting the form with the sire/dam IDs (or using the direct url above) you should get the summary page for the analysis.
At its simplest, click the View Report link next to Coefficient of Inbreeding to display the COI for the lamb born by mating a ewe to her son.
This Inbreeding Loop Analysis is an interesting report that lists all the “inbreeding loops” found in the pedigree. Inbreeding loops are basically a path from an ancestor on the sire side through the base animal to the same animal on the dam side. In this simple example, there is one inbreeding loop from the dam to the sire’s dam. Using Wright’s formula for COI yields a COI value of 0.25 for this loop. More complex examples can have many loops, as you will see in Example 3.
The Summary Page also provides links to several detailed reports, grouped together in the second gray box on that page:
Total Ancestors Report is basically the complete pedigree from the database in table form, with one line per ancestor. In this simple example, there are only 4 ancestors. Click the blue 
link to the right of Total Ancestors Found to view the list. You can also click the View Pedigree link below the table to bring up a pedigree for this hypothetical mating in a new browser tab. Take a look at that pedigree; it is easier to visualize than the list. You might find the full list to be useful for complex cases where you want to see farther back than the 5-generation pedigree.
In the Total Ancestors report, the Gen column shows how many generations back each animal is from the root animal. And the Label column indicates the exact position of the animal in the pedigree. For example “S” is the sire, “SS” is the sire’s sire, “SD” is the sire’s dam, etc.
In this example, you can see from the pedigree that the animal’s dam (D) is the same ewe as the animal’s sire’s dam (SD) (dam mated to her son).
Note: When looking at any of the detailed reports you can use the Back to Pedigree Analysis link at the upper right to return to the main page.
The Unique Ancestors, Common Ancestors, and Duplicate Ancestors reports provide subsets of the Total Ancestors list and might be useful in more complex cases. For example, the Common Ancestors report shows all animals that appear more than once in the pedigree and the count of how many times they appear.
Example 2: Mating of full siblings (sire ID #0364, dam ID #0485)
https://www.blackbellysheep.org/db/members/analyze.php?said=0364&submitSDAID=Go&daid=0485
This example is a little more interesting. The reports reveal two inbreeding loops: one from sire’s dam to dam’s dam, the other from sire’s sire to dam’s sire. The COI values for the two loops are simply summed together to get the total COI of 0.25.
Example 3: Mating of half siblings (sire ID #0364, dam ID #0376)
https://www.blackbellysheep.org/db/members/analyze.php?said=0364&submitSDAID=Go&daid=0376
This example has just one loop from sire’s sire to dam’s sire, yielding a total COI of 0.125.
Example 4: Complex example of a single animal (ID # 4397)
https://www.blackbellysheep.org/db/members/analyze.php?aid=4397
The various reports for this case reveal how complex this process can be. This animal has 11 generations of ancestors (448 total) in the system, and there are a whopping 809 inbreeding loops in the pedigree. These loops condense down to 25 different COI component parts (one for each common ancestor from the inbreeding loops). The COI report shows how they are summed to obtain a total COI value of ~0.3438.