It’s been years honestly since I even bothered with them after the initial instance where I actually sent the same sample in twice and got different results. I’m not sure who it was, I just don’t trust those machines
I sent two tests in for my display tank and my frag tank and they were pretty close as far as the major elements that we can test for (can't test for trace elements). My basement refractometer was out of calibration which is why the make up water in the 30 gallon Brute was 32 ppt instead of 35ppt. I just calibrated it with new Brightwell seawater calibration fluid.