Hydrometer vs Refractometer

[Johnny Reefer]

I have both, but haven't used the hydrometer in about 3 years. I always use the refractometer and will continue to do so. But a question comes to mind....if the error of a hydrometer is known, could the hydrometer not still be used and just simply apply the error in calculating the true reading?...or is an error in a hydrometer prone to fluctuate? (This is assuming the instrument is cleaned thoroughly after each use).

Cheers,