How is the average position calculated?
Average rank or adjusted average rank is a sum of all rankings divided by the number of keywords you’re tracking for a particular URL or website. For a better representation and comparison, we use a maximum search depth ranking (100 in most cases) for the keywords that are not ranking anywhere in the searched results.

How is search volume defined?
Search volume is defined as average monthly searches for a particular keyword on Google. One is global search volume (the total number of all searches globally) and local, based on the keyword location you're tracking.

How is click potential calculated?
A certain keyword's click potential is calculated by the number of local searches for this keyword (local search volume) multiplied by an average CTR for that keyword ranking on Google. It is a good indicator of how many clicks you should be getting when ranking on the first page of SERP.

How is the search visibility index calculated?
The search visibility index is a metric representing the percentage (values between 0 and 100) of potential conversion traffic a given keyword (or set of keywords) has based on its ranking. Based on each ranking, the CTR value is applied.

CTR rates that we use for calculating click potential and search visibility (as of Dec 14th, 2018):

There are other factors involved that will affect your search visibility score:

Also, if:

Then the Search Visibility will be 0.

Click here to check out the article on reading keyword data.