(Update - see comments - Zoe won!)
I'm totally stumped - I've bought some of these adjustable dog leads and I can't make head nor tail of them. How do they work?

The first person to email me with an explanation as to how to use this -  I'll send you one for free!

Please click here to email me 


This is what it looks like
There is a trigger clasp at either end and in between 3 rings which can be moved up and down the lead. 

Strangely, one large ring  in the middle and two smaller ones either side so  I guess the difference in size must be for some reason, too???

HELP, pretty please