Hey, regarding the picture of the hydrometer you gave. Use that thing. Dairy hydrometers (as they're often referred to) work on the same principle as the plastic cheap hydrometers with the floating needle inside. That is to say they work on relative density. But whereas the plastic floating needle hydrometers are crap and should only ever be used to measure your cars radiator fluid, glass dairy hydrometers are the most reliable density measuring equipment available. That is why labs use them all the time. And best if all, they don't need to be recalibrated all the time like a Refractometer does.
Finally, best if all, your hydrometer is scaled for your application. Ranging from pure water to salt water (1.000 to 1.026) on most Refractometers is about 3/8 of an inch. Your hydrometer looks to be about 1 inch or do for the same range.
Don't get me wrong, refractometers are the next best thing because they are easily calibrated and give a repeatable result. But you will barely be able to tell the difference between 1.025 and 1.026. My brewing dairy hydrometer was just as accurate and never needed to be calibrated.
I would not buy a refractometer if I had a glass hydrometer on hand.
