The Brix refractometer shows the concentration percentage of the soluble solids content (Total solids) of a sample (water solution). The soluble solids content is the total of all the solids dissolved in the water - beginning with sugar, salts, protein, acids, etc. and the measurement reading value is the value of the sum total of those. Essentially Brix% is calibrated to the number of grams of cane sugar contained in 100 g of cane sugar solution. So, when measuring a sugar solution, the Brix% should perfectly match the actual concentration.