Hydrometer for the 19-Set

[David Dunlop]

I have seen two versions of this item: one that fits in a rather POSH looking wooden box, and the second (perhaps a slightly smaller item) that stores in a simple cardboard tube, either blue or grey, with an instruction label glued on the outside.

Were these only issued/needed when the 19-Set was installed in a Command or Signals Vehicle where portable batteries were an issue?

And are the two types fully interchangeable, wherever needed?

David