Czech wine of these festivals in Znojmo, Mikulov, Brno and Mělník will feature samples of hundreds of local wines as well as local music, dancing and cuisine. These wine-festivals take place in big towns apart from the wine-producing areas as well (such as Prague). Czech wine law classifies wine according to the origin of the grapes and the ripeness of the grapes determined by measuring the must weight in the grape juice at the time of harvest. Sugar content is expressed in units of °NM on the Czecho-Slovak Normalised Must-Weight Scale (Czech: "Normalizovaný moštoměr"), which indicates how many kilograms of sugar are
Brix prism; the result is observed through an eyepiece. The critical angle (the angle beyond which light is totally reflected back into the sample) is a function of the refractive index and the operator detects this critical angle by noting where a dark-bright boundary falls on an engraved scale. The scale can be calibrated in Brix or refractive index. Often the prism mount contains a thermometer which can be used to correct to 20 °C in situations where measurement cannot be made at exactly that temperature. These instruments are available in bench and handheld versions. Digital refractometers also find the critical