I asked once.
The fella said he just tried to record as many registrations as he could. He was aiming to be able to say he had seen more aircraft on the G reg than anyone else.
Stange thing is I asked him about Sia's - he knew everone on the UK register by registration alone I am convinced - worrying, very worrying.
Of course there are some tecnical terms you need to know and this thread is apparently about:
"Graphing an aircraft"
But you will also need to understand:
"Poling off"
"Clearing a drome"
"Pond hopper"
and
"Fleeting"
Please dont ask me how I know!