Fact is there are many different ways to park a plane, from self manoeuvre through marshalling to all walking talking Visual Docking Guidance Systems.
In the UK there are no common types at the majors (sorry Brissol) meaning that foreign crews have to scrath their heads to guess which system they will find on different stands.
AGNIS (Azimuth Guidance Nose in Stands) is provided primarily to align the nose wheel on the centre line.
PAPA (Parallax Aircraft Parking Aid) is the blackboard with vertical white lines and a/c type flags to tell the pilot when to stop. It works by the apparent progress of an illuminted strip across the board when viewed from the cockpit as the a/c approached the head of stand.
Mirror docking is another aid to stopping that gives the Capt a view of his nosewheel and has reversed a/c types painted on the floor that appear correctly in the mirror.
Trouble is...and it's with a capital T all of these only work to the left hand seat. So the P2 will always struggle to stop without help from P1.
Also the 2 aids to stopping are not colocated with the AGNIS requiring heads to turn in order to asymilate the whole picture.
ICAO now recommend against this.
The development of advanced laser, ladar and camera systems that are ICAO compliant and usable from either flight deck seat is now well advanced, and there are plenty of them around the world. It is a pity that progress in the UK has been lagging behind the rest of the world. Would'nt be the bean counters would it?
Finally, as a marshaller once said to me "Captain, the brakes are under your feet not on the end of me bats!!!"
Sir George Cayley