What are they and how are they used?
A refractometer is an instrument with a prism through which the light can shine and give a reading on a graff that can be viewed through the eyepiece which can be adjusted for proper focus. The angle of the light shining through the prism is affected by a thin layer of juice or pulp from whatever food you are testing. The amount of solids (which will include sugars and minerals) will show up as a reading on the scale. Here is a picture of the view you would see when testing the pulp of a fruit.
We have a high quality refractometer which is available for $75.00 and can be ordered by phone (828-649-0070), email (email@example.com), or by mail (Medical Missionary Press, 474 Blue Hill Road, Marshall, NC 28753).