Polarimeters are an optical instruments used for measuring the angle of rotation plane of polarization of light polarized through the solution of the test substance. One of the best known types of polarimeters is manual half shadow-circular polarimeter (model WXG-4), which allows clear determination of the polarization plane, measurement is done by setting the analyzer in such a way that the two halves of the wheel in the field of view have the same brightness. After inserting the polarimeter tube with the solution image changes, because the solution caused the rotation of the plane of polarization. By turning the rotary dial we adjust the field of view again to a uniform darkening of three parts of the field of view. The difference between the angle read out in this position, and that of a polarimeter zero is equal to twist angle.
Semi-automatic polarimeter (model PLRS-5) or automatic (P series or series FTU) allow increased automation of measurement which significantly shortens the time of performed analysis. The measurement results are automatically displayed on the LCD monitor. This provides the ability to quickly read the result and eliminate the inconvenience associated with analog readout. Automatic laboratory polarimeters are characterized by high sensitivity, ease of use and reading of results.