Good advice.
Checking/verifying numbers is good practice.
An LFS and/or tank maintenance service burns through reagent fairly quickly with multiple tank water samples. They usually notice right away, by referring back to the testing history, when a bottle of faulty reagent has been received/used.
Along this same line, not too long ago I was checking salinity of the water in the bag holding a fish from Rusty's Reefs. It was way high, like 1.030.
But it wasn't what I thought. The problem was with me. My refractometer was off. Turns out that Rusty had compared three separate salinty standard solutions from three separate manufacturers. They each agreed.
Since then I have compared refractometers and hydrometers that I come across, finding all of them to be reading wrong, mostly too high. Even when calibrated with pure water, they are wrong, as was mine!
But so what. It doesn't really matter much. Fish and coral can live just fine in salinity(specific gravity) anywhere between 1.018 and 1.030 and they tolerate modest variations that come quickly. Currents can bring water of varying specific gravity and heavy storms can dump so much fresh water that there can be a significant drop in salinity in a very short amount of time.
It's not a bad idea to always check the salinity of the water surrounding a newly acquired animal and adjust accordingly. I do not suggest drip acclimation as that causes more problems than it solves. I just take a few more minutes to acclimate an animal to higher salinity.
Aloha,
Mark