[Richard Coutts-Smith]

Thanks Mike, thought you would be one of the few able to help.
Hard to say if many were made, but as this is serial N0.26, I assume that there were at least 25 others.
The unit is sealed when closed up, and would be quite waterproof, to the point that it would appear to be able to float, this would tie in with the 153 set shown in its waterproof case.
I have passed on your reply on to the current owner, now he knows what it is he can decide what to do with it.
Best Regards
Rich.