The front view of the target has focus area and alongside it a sloping ruler to determine where the actual focus lies. The centre AF point is aimed at the main target for testing, with the rear alignment just visible through the small hole in the centre.
In the photograph below (600mm f4 at f4 at 25 times focal length distance) the focus is clearly behind the target. Adjustment is made in the camera menu and the camera lens combination can be forced to focus correctly. The camera memorises the serial number of the lens and changes the adjustment to suit each individual lens and up to 20 can be stored. Images are made in monochrome to allow ease of assessment and against a dark background and maybe over sharpened to evaluate the focus area. Trial and error is required and the lens should be sent through it full movement range between each test.
A chore but the results are noticeable when completed.