We developed a low-pressure interferometric liquid piezometer aimed at the determination of correction to the density of the working liquid of a laser interferometric oil manometer used as a component of the GET 101-2011 State Primary Pressure Standard for the range of absolute pressure 0.1-7.10(5) Pa. The indicated correction is caused by the compressibility of the working liquid. The comparison of the obtained correction with changes in the density of the working liquid as a result of its deep degassing (measured at the Physical Technical Institute, Germany) shows that, under the working conditions of the laser interferometric oil manometer, these two effects compensate each other almost completely. This confirms the reliability of the results of pressure measurements within the range 0.1-10(3) Pa performed by using the GET 101-2011.