Polarimeters measure how far a sample rotates plane-polarised light, which reveals the concentration, purity and chirality of optically active compounds such as sugars, amino acids and pharmaceutical actives. Manual models read rotation by eye against a scale, semi-automatic units add electronic readout, and automatic polarimeters report optical rotation, specific rotation, concentration and sugar degree to 0.001 degrees at the 589.3 nm sodium D line. Peltier temperature control on automatic models holds the sample steady, since specific rotation shifts with heat. Typical uses include sugar content in food and beverages, enantiomeric purity in pharmaceuticals and essential oil analysis.