Found recently this hydrometer – range 900–1000 - is in perfect working order and is in its original packaging.  Though there is no date on it, I would say that it is probably pre-1960’s.

If you have any questions, feel free to ask, though I can’t give much more info than is already here and can be seen in the photograph.

Due to the item containing mercury, this will be a collection only sale.  I am based in central London.