  A criterion for assessing the reliability of measurements of the Sachs form
factor ratio using the Rosenbluth technique is proposed and applied to an
analysis of three known experiments (Andivahis1994, Walker1994, Qattan2005) and
a recent experiment on the CEBAF accelerator upgraded to 12 GeV at JLab
(arXiv:2103.01842 [nucl-ex]). Based on the results of the JLab polarization
experiments on measuring the ratio $\mu_p G_E/G_M$ in the $\vec e p \to e \vec
p$ process, in the kinematics of the SANE Collaboration experiment (2020) on
the measurement of double spin asymmetry in the $\vec e \vec p \to e p$ process
numerical calculations are performed for the $Q^2$ dependence of polarization
transferred to the proton in the $e \vec p \to e \vec p$ process when the
initial proton at rest is partially polarized along the direction of motion of
the detected recoil proton.
