  The available experimental information on the Range-Energy relation for
protons stopped in hydrogen gas is summarized in the SRIM software package. The
estimated precision of this data is several percents. Here we describe a
possibility to measure this relation with 0.1$\%$ precision in the course of an
electron-proton elastic scattering experiment to be performed in the 720 MeV
electron beam at the Mainz Microtron (MAMI). This experiment, aimed at
precision measurement of the proton charge radius, exploits a large hydrogen
"active target" to detect the recoiled protons and a forward tracker to detect
the scattered electrons. The angles of the scattered electrons are measured
with $2\cdot10^{-4}$ absolute precision. Also, the electron beam momentum is
known at MAMI with $2\cdot10^{-4}$ absolute precision. This gives a possibility
to determine with 0.1$\%$ absolute precision the four-momentum transfer $Q^2$
which, in its turn, is a direct measure of the recoiled proton energy $T_{p}$:
$Q^2 = 2M_{p}T_{p}$, where M$_{p}$ is the proton mass. From this point of view,
this experimental setup can be considered as a source of protons with well
defined energies inside an "active target", which is a specially designed
hydrogen high-pressure Time Projection Chamber (TPC). The design of the TPC
allows to measure with high precision the energy of the protons corresponding
to some selected values of the proton range. In this way, the Range-Energy
relation can be established for the proton energies from 1 MeV to 9.3 MeV with
0.1$\%$ absolute precision, the maximal energy being limited by the size of the
TPC and by the hydrogen gas pressure.
