The service level shows how many userposts get a reaction by the page in form of a like, a comment or deletion. Reactions on “regular page posts” (published by the page itself) do not count.
Example: Page A got 20 userposts within the chosen period of time. 4 of them got a like, 5 a comment and 2 were deleted; 11 userposts got a reaction, which equals 55% ( 11 / 20 * 100 = 55).