Refractometer is another name for it, the scale can vary both in range, and units. Brix is a common scale, calibrated for sugar in water for the beverage industry, with conversions, or dedicated units with a scale appropriate for the sample being measured.
I.e. The refractometer that a machine coolant vendor sells you will of course read directly for the oil emulsion, but an ebay/amazon one in brix may not.