Digital Refractometer PSU must be = ppt ?

[Charles Silva]

Hello all

I'm doing some tests with a Hanna HI96822 Digital Refractometer for Seawater Analysis and I get 1 unit diference when switching from PSU to ppt scale using the same sample. Shouldn't be equal the results ? @Hanna Instruments

 

[Randy Holmes-Farley Verified Community Expert]

Yes, for reef hobbyist purposed, 1 PSU = 1 ppt. But it is not exact as they have different definitions.