Must weights are commonly measured in the vineyard to monitor the
ripeness of the grapes, which helps select the time of harvest. For this purpose, it is usually measured by using a
refractometer. A few grapes are crushed between the fingers and the must is dripped onto the glass of the refractometer. The refractometer will be calibrated in a must weight scale, but as refractometers actually measure
refractive index (of the grape must in this case), the must weight scale on the refractometer is in effect an indirect measurement, with refractive indices having been pre-converted to their must weight equivalents. ==See also==