SG and PPT in refractometer

[hillegom]

Originally Posted by mrhasan

Sorry for getting back to this thread after a long time.

Anyway, my question was that in various forums, I always see people telling to measure PPT instead of SG and that's where I am scratching my head. Like does SG scale move up or down and ppt remains fixed? Because as far as I can see, the scale is fixed while for ATC, the metal strip expands or contracts for temperature compensation to show 1.026 - 35ppt ratio. Is measuring SG and PPT the same in a ATC refrac then?

I'm at a loss. I have never taken one apart. There is a metal strip inside?
I have always believed (but not known) that the scale had something to do with how the light refracted off, who knows what. The metal strip?
I'll have to do some research when not so busy.