Texture aspect ratio

[cattz]

I'm trying to understand how the texture aspect ratio box works. Whatever I type in the top or bottom box that size is repeated in the opposite box, that bit I understand. Now if I want to change the ratio clicking the chain symbol (breaks) but as soon as I move the mouse the chain is locked again so I can't find a way to alter the ratio.
There is obviously a correct order to do this so some advise would be appreciated. Thank you.

Sorry, I think I've found the answer myself. I was double clicking (habit!!) the chain icon not single click. Now works just as it should.

[TIG]

Material Broswer: Texture Size settings...

Click the chain to toggle it from unbroken/broken.
With an unbroken chain the edited sizes change in proportion, e.g. make one twice as big the other one changes to twice its size to match.
With a broken chain you can change edit one size and the other size will remain as it is.
Making the chain unbroken again will re-link them ,and once again they change in proportion; although at this point you may well have got two unequal sizes they will still be changing 'proportionally' - e.g. twice the size...