  An eight stage balanced modulation scheme for dual beam polarimetry is
presented in this paper. The four Stokes parameters are weighted equally in all
the eight stages of modulation resulting in total polarimetric efficiency of
unity. The gain table error inherent in dual beam system is reduced by using
the well known beam swapping technique. The wavelength dependent polarimetric
efficiencies of Stokes parameters due to the chromatic nature of the waveplates
are presented. The proposed modulation scheme produces better Stokes $Q$ and
$V$ efficiencies for wavelengths larger than the design wavelength whereas
Stokes $U$ has better efficiency in the shorter wavelength region. Calibration
of the polarimeter installed as a backend instrument of the Kodaikanal Tower
Telescope is presented. It is found through computer simulation that a 14% sky
transparency variation during calibration of the polarimeter can introduce
$\approx 1.8%$ uncertainty in the determination of its response matrix.
