I ordered a refractometer from Age of Aquariums last week, and it turned up today.

Refractometer

This device is used to measure the salinity of water, which is going to become quite handy in my upcoming reef tank project. I decided to get this rather than a hydrometer as using a refractometer is far more accurate and only requires a few drops of water, where as a hydrometer requires quite a bit of water to float it.

Besides, it also looks all cool and scientific. ;)