Thanks mrsnipey
That's a great explanation.
I must now remember to pack some blutack in my kit so I can stick the ring to the base, because knowing my luck I'll probably "kick" it around while I'm observing/wandering
.
Everybody here is so helpful, it will make me look like I know what I'm doing when I get out there (except Chris and Rob will probably remember what I was like last time
)