Just calibrated two Refractometers

I agree and disagree with calibration solution. Other than the label, there's absolutely nothing else that tells you the accuracy of the solution let alone it being a bad batch of solution. Now of course a single hydrometer has a ton room for error. My personal feeling on it, as a mechanic, is that the float type hydrometer will never change it's weight from the day it was sealed in glass unless the glass breaks. The scale card that's in it could definitely be off but it will still float at the different levels of specific gravity and land on those same spots. So my method of madness is to compare a few hydrometers and/or refractometers that have been calibrated properly. using that information of setting a batch of mixed water to, I just drop my floating hydrometer in the water and mark the spot that it floats up to with a marker and that is now my specific gravity I use and stick with. No headaches of calibration anymore. I'm not saying that what people are doing are wrong. it's just my method to my madness lol. I just know that we aren't dealing with medical grade equipment and my trust in companies to make batch after batch of good calibration solution is not there.

 

Looking through the Marine Depot catalog I see different Refractometers. Their "Pro" Refractometer clearly states calibrate with calibration fluid. Just looking at the picture it appears to be the same one BRS sells just a different color.
For the standard refractometer it says calibrate with distilled water. Not sure what the difference is but evidently these instructions are a must because my Pro version must use calibration fluid or it will not be reading correctly.
For my standard refractometer both methods work.