Hydrometers are handy, but if all you're looking for is density, an accurate scale used on an accurate volume at a specified temperature will get you the same information. For example, I use my battery electrolyte hydrometer for a quick check of status. But if I really want good data, my triple pan balance comes out, along with a calibrated flask. I found it interesting that the hydrometer had both accuracy and repeatability problems.
I figure many of you will have (or have access to) a decent scale.
Finest regards,
troy