Also don't forget the most important salinity. Most of us go out and buy a refractometer and swear by it to give us accurate reading. Happened to me and was running my tank at 1.031 for long time. Although it did not cause massive die off but a third of my new additions didn't make it. Turn out that my refractometer is out and cannot be cal properly.
With regards to calibration, most will want you to cal using di/ro or distilled water at 20degrees. Firstly, a stable 20 degree is not easy to achieve at home. Second, if you are given a choice of a one point calibration, sg of 1.000 is far away from our target measurement of 1.026. Engineering will tell you that if a one point cal is the only choice, you will do it at the point of the target measurement. Even if your meter's span is out, it will still be accurate at sg 1.026.
Now I am only using a salinity standard solution to cal my refractometer. Pinpoint do have one that is 1.026. With this you will not require 20 degree room temperature and can be performed at room temperature.