Originally Posted by nasmeyer
I just checked my hydrometer in 60 degree distilled water, and got a reading of 1.004. I would have to believe I calibrated it when it was new but don't remember doing so. Can a hydrometer become un-calibrated without actually breaking the glass? I would have to think that anything that would dislodge the paper would also break the glass.
Well, many hydrometers are calibrated to 68°, but you're right that 4 points is too big a difference.
Short answer is, yes, the paper inside isn't secured (in any hydrometer I've used), and CAN slip. I wasn't even aware of it until I noticed one of mine slipped drastically.
Luckily it's all linear, and you can just subtract 4 points from any reading.