A digital handheld refractometer is an instrument for measuring the refractive index of materials.
Most operate on the same general critical angle principle as a traditional handheld refractometer.
Once the position of the shadow line has been automatically determined by the instrument, the internal software will correlate the position to refractive index, or to another unit of measure related to refractive index, and display a digital readout on an LCD or LED scale.
Nearly all digital refractometers feature Automatic Temperature Compensation (for Brix at least) Most have a metal sample well around the prism, which makes it easier to clean sticky samples, and some instruments offer software to prevent extreme ambient light from interfering with readings (you can also shade the prism area to prevent this as well).
There are some digital handheld refractometers that are IP65 (IP Code) water-resistant, and thus washable under a running faucet.