If I can remember this right, most Hydrometers are calibrated for 60 degrees f. Cold water has a higher density than warm water, and that works out to ~.001 difference per 10df. In other words, for most hydrometers, if you're measuring 1.0023, a refrac would put that at ~1.0025. This leads many people to say "WHOA!" when they see their results from a refrac, and assume that their hydrometer was bad. Not always true.
When we tested our hydrometer against a calibrated refrac, we were .003 out (so, .001 adjusted). It was very consistent over multiple tests, on various sources, so we now trust our hydrometer (and make the necessary adjustment). Not perfect, but close enough for jazz.
On the other hand, many people note that the refractometers are now so cheap, why not buy one? Not bad advice at all.
Matthew
|