Engineering Physics Annotation << Back LG – unrotor gyro with momentum B.V. Melkoumian Different explanations of the Sagnac effect and cause of the systematic errors of the laser gyro (LG) are discussed. Here is shown that the «gyroscopic effect» in LG, as in any other gyroscope, exists due to the presence of certain momentum of light in a resonator up to its rotation. Due to conservation law of momentum with rotation of the resonator with reference to the inertial system this momentum took a different position in the system and changes its energy. The classical theory allowed us to determine the quantum restriction of sensitivity of LG, an additive error of the scale factor of LG and to show that the «zone of capture», or «dead zone» on the output characteristics of LG exists due to the precession of vector of momentum around the angular velocity vector, acting on baghron of light in the ring laser resonator. Key words: laser gyro (LG), momentum of pulse, systematic measurement errors of LG, precession of momentum, angular velocity. E-mail: BMelkumyan@miemp.ru. Pp. 3-12.