The WM-7 with 7 scales is a pocket Digital Wine Refractometer designed to operate of under the strictest environmental conditions, especially areas of high humidity of production and to measure concentration of grape must, easily, speedily, and accurately. Measurement of grape must concentration can be taken by winegrowers, wine cooperatives, wineries, buyers for grape must and so on. The measurement accuracy is upgraded to Brix ± 0.1%. Equipped with a new technology “External-Light-Interference” (E. L.I.)* that enable you to take accurate measurements with ease and confidence near at a window or outside. *Patent Pending