Some electrooptic and thermooptic effects of cholesteric phase are used in liquid crystal visualisation and display systems provided spiral pitch is equal to a visible wavelength or several micrometers. Liquid crystals with cholesteric properties were generally cholesteric esters. Unfortunately these materials are chemically non-stable. More stable nematic liquid crystals twisted by mixing with chiral materials or by adding assimetric side chain have also cholesteric phase. In this case spiral pitch depends on many factors. This report unites theoretically predicted temperature and concentration dependence of pitch and compares it with some original or known results.