be higher in calcium, which neutralizes acids. However, the blue background can be overcast by the deep green chlorophyll color of some leafy plants.  Do not be discouraged if your field of view appears to "greenout."  Simply rotate your body away from the light source and watch for the demarcation as the light intensity diminishes. Although your mouth readily tells the difference, the refractometer cannot easily distinguish starch from sugar. There is an additional chart in the book to convert starchy food readings to sugar equivalents. Some produce resists efforts to get a drop of juice for testing: Consider that it may be very high brix and that the juice is really thick. Try cutting a very thin slice (1/16" to lay on the prism---it really works!), or Crush a leaf and lay that on the prism, or Grind the food in a processor and squeeze the chopped result. Be wary of dehydrated produce. Some foods are made to order for testing: You can plunge the prism end of many refractometers into citrus fruits. Then pull the instrument back and flip the plate down to get the reading. (The plunge method works well on other very ripe fruits and any tomatoes). (*) Protein quality is a subject of much interest to farmers.  Should you ever visit a farm show devoted to biological growing, as opposed to chemical growing, you are almost sure to find a booth where they have common ear corn sealed in air-tight jars.  As could be expected,