Found recently this Twaddle's Hydrometer No.3 – range 1000–1150 - is in perfect working order.  It 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.

I can't get the picture to uplaod.  If you are interested, please contact me, including your email address, and i will send the picture to you.