A polarimeter ^[1] is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.^[2]

Some chemical substances are optically active, and polarized (unidirectional) light will rotate either to the left (counter-clockwise) or right (clockwise) when passed through these substances. The amount by which the light is rotated is known as the angle of rotation.

A saccharimeter is an instrument for measuring the concentration of sugar solutions.

This is commonly achieved using a measurement of refractive index (refractometer) or the angle of rotation of polarization of optically active sugars (polarimeter).

Saccharimeters are used in food processing industries, brewing, and the distilled alcoholic drinks industry.