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It was originally made for measuring blood serum or urine, however there is a general scale with the serum scale on the side. So you can use it to measure any other things, such as wine, fishtank salinity, etc etc. All you need is a conversion table, which are readily available for most commonly sought characteristics.
The refraction scale is from 0 to 320 (32%), 2 (0.2%) intervals. The image is very clear when viewed against a light. A manual is included.
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(Click on the thumbnail images to enlarge)