Hanna Instruments digital refractometer for refractive index directly, one model.
HI96800
This Hanna Instruments digital refractometer measures refractive index directly, alongside the Brix scale.
Refractive index is the underlying physical property; every other scale is a conversion from it for one particular substance. Reading it raw lets the instrument be used on anything, including materials no sugar scale was ever written for.
Light bends by a different amount depending on how much is dissolved in a liquid. A refractometer measures that bend and converts it to a concentration scale. It needs one or two drops, gives an answer in seconds, and has no reagents and nothing to consume.
A digital instrument compensates for temperature automatically, which is the difference that matters: refractive index shifts with temperature enough that an uncompensated reading in a warm room is simply wrong.
Refractive index is strongly temperature dependent; quote the temperature with the value or the number means little.
Supplied as one model.