A key thing to learn is your own adjustment factor using the calculators on Sean Terrill's site. He says the average for many people was 1.04 for the correction factor, but for my gauge I found it is most accurate with a factor of 0.98 as compared with the hydrometer. YMMV. Learn your magic factor and then you too can use the refractometer semi-reliably, i.e., "good enough".