Things to consider, these may be obvious but I'll mention them. High or low salinity, or should I say "relative salinity" based on what ever calibration method used, should just be that, high or low, and shouldn't change. Or if it does gradually to middle ground (only because that is where there is more room for error). Also remember, your salinity will amazingly "change" as your sample drops in temperature (remember it's specific gravity) as temperature is our measuring guide. Don't compare sample's of different temp!
In nature, especially off shallow reefs, salinity and temperature changes can not only be felt (as in temp) but seen. It's like looking through a mirage, and the fish and coral don't mind.