  We present a characterization of CasPol, a dual-beam polarimeter mounted at
the 2.15 meter Jorge Sahade Telescope, located at the Complejo Astron\'omico El
Leoncito, Argentina. The telescope is one of the few available meter-sized
optical telescopes located in the Southern Hemisphere hosting a polarimeter. To
carry out this work we collected photo-polarimetric data along five observing
campaigns, the first one during January, 2014, and the remaining ones spread
between August, 2017 and March, 2018. The data were taken through the
Johnson-Cousins V, R and I filters. Along the campaigns, we observed eight
unpolarized and four polarized standard stars. Our analysis begun
characterizing the impact of seeing and aperture into the polarimetric
measurements, defining an optimum aperture extraction and setting a clear limit
for seeing conditions. Then, we used the unpolarized standard stars to
characterize the level of instrumental polarization, and to assess the presence
of polarization dependent on the position across the charge coupled-device.
Polarized standard stars were investigated to quantify the stability of the
instrument with wavelength. Specifically, we find that the overall instrumental
polarization of CasPol is $\sim 0.2 \%$ in the V, R and I bands, with a
negligible polarization dependence on the position of the stars on the
detector. The stability of the half-wave plate retarder is about 0.35 degrees,
making CasPol comparable to already existing instruments. We also provide new
measurements in the three photometric bands for both the unpolarized and
polarized standard stars. Finally, we show scientific results, illustrating the
capabilities of CasPol for precision polarimetry of relatively faint objects.
