>John Woodgate wrote:

> 200 x 200 mm is quite a big lump of metal. That must be uncommon. If
> they gave the range for, say, a typical coin, it would perhaps be about
> 20 cm in some soils.

Yes it is indeed a big lump of metal though the detector in question has
been designed specifically to find large buried objects.
I gather it is supposed to be used where a normal detector has come across a
number of coins in a small area and so is used to locate a potential hoard
at a greater depth.

Though the thought of anyone digging down 3m in the middle of a ploughed
field is some task, then perhaps not if you have hired a JCB to do the job.
;-)