The measurement principle behind KEM refractometers is based on the Abbe refractometer.
In typical Abbe refractometers, the light/dark boundary corresponding to the critical angle is detected manually.
In contrast, with KEM refractometers, the light reflected at the interface between the sample and prism is received by a CCD, and the critical angle is automatically detected from this signal.
If using an Abbe refractometer is prescribed in a set of standards, a KEM refractometer can be applied.