Howdy.

I have an ATC refractometer. At first I thought the unit had a defect, and maybe it does, but I'm starting to wonder.

The line where the white and blue meets in my refractometer is at a slant. This is why I thought it was a defect. But as I understand it, specific gravity (e.g., 1.025) changes with temperature whereas salinity (e.g., 35 ppt) does not. Mine displays both specific gravity (left scale) and salinity (right scale) side-by-side. Since the salinity is always 35 ppt, the line has to be at a slant to account for changes in temperature for specific gravity.

Is this right? Is a slant expected in the blue/white border?

I'm at work, but I'm thinking about testing this tonight with chilled (fridge) and warmed (microwave) saltwater.

Thanks.

The refractometers I have used all had a horizontal line and they were also graduated in salinity/SG.

Refractometers don't measure "salinity" or specific gravity, they measure refractive index. Refractive index is also influenced by temperature.

The slant indicates some type of problem in alignment (check if the eyepiece got tilted).

The "ATC" in your refractometer's description indicates automatic temperature compensation. However, that usually doesn't mean it will compensate for very large temperature ranges like chilled saltwater. Usually more expensive refractometers have higher ATC ranges.

Watching as mine has the same look. Tilt is slight but it's there, just a tad higher on right side than left.

They should be horizontal.