The numbers are an indication of the total number of articles/documents within that category that match your search. It takes into account all possible matches, strong or weak when coming up with the number.
When you click on a filter to narrow your choices, the Spirent Knoweldge Base does further analysis to determine which results to show. Only the documents still considered a strong enough match will be shown; this can mean the number of results shown are less than the count shown on the filter category. Please note that this is done to maintain the highest search performance possible.
To improve your searches, we have some search tips and tricks.