Nx measures / compares produce quality.
For 200 years, the best 'objective' measure of produce quali
.. has been nutrient density using optical refraction.
BRIX meters have been accepted as the best 'objective' measure of produce quality for by Food Scientists and Health Authorities.
The higher the degree of refraction due to the density of liquids, juices, sap, etc., the greater the nutrient density, the more delicious and nutritious the produce!
But this is a messy and time consuming business, not possible to do in a food store or at a Farmer's Market.
But has been used by Australian farmers for past 90 years to improve their crop or grasses qualities by annually improving soil inputs.
More info on BRIX meters and refraction can be found here