Scarva Tools Large Glaze Hydrometer  £25.46

I have only done a quick test against my tutor's hydrometer, using one glaze, but it worked well. It would be handy to have specific gravity as well as Baume measurements on it. Lots of info on line if you need to know the difference and how to use it (no instructions sent with the item).

Useful item to have, this functions exactly as it should, in protective tube and well constructed bit of kit.