First and foremost, I believe in buying the best equipment that I can. I think its worth taking a little extra time to save a little extra change to get “the next step up” when it comes to certain pieces of equipment. My main reason for that is because proper calibration then becomes less of a concern.
And that brings me to some bad news for everyone… you CANNOT CALIBRATE a hydrometer or thermometer. Calibration by definition, testing a known sample then SETTING that equipment to the known sample. There is no way to RESET a hydrometer or thermometer. These are preset closed instruments that were pre-calibrated by the manufacturer (hopefully correctly, see the opening paragraph).
Now before I get a lot of nasty comments about calibration, you can do what is referred to as Correction. You can test your hydrometer in 60F distilled water for its accuracy at zero. You can also test it in water with a pre-weighed amount of sugar to a desired gravity (assuming your scale is accurately calibrated too! You may be able to calibrate your scale). If the hydrometer doesn’t read zero where its supposed to you can determine a Correction factor. Which means you know that at zero water your hydrometer reads 1.004. That means to get to true zero you need to subtract 4 points from your reading. That means that a 1.054 reading is actually 1.050 SG. What you have just done is determined your equipments correction factor and you need to work that into your brewing notes.
I know many people refer to that process as calibration, but as I lab guy I have to stand strong here and say that it’s not.
The last problem with using correction is that sometimes instruments do not react linearly across the whole scale. Meaning that although your hydrometer reads 1.004 at “1.000” that doesn’t necessarily mean that it is going to be off by 4 points at all gravities. (1.054 for 1.050 and 1.074 and 1.070) In fact it usually gets worse as you move away from zero. So the best thing to do is make a solution of sugar water to a specific gravity at the highest you normally brew at and something in the middle (say 1.085 and 1.040). You can then see if the drift is up or down as you go up the scale and adjust accordingly with future, “real world” samples.
It’s not the end of the world, it’s just something to be aware of and how to deal with it; functionally and terminologically (is that a word???). At least now you have a good argument for chat over the brew kettle with your buddies next time.