Polarimetric observations were possible in one PHT-P (at 25
m)
and one PHT-C filter (at 170m). Measurements were always made
for all three polarisers together with (1) a non-polarised measurement
to determine the total intensity and (2) an FCS measurement for photometric
calibration. At least two cycles of measurements in the three polarisers
were collected in order to obtain sufficient redundancy for signal
assessment. The PHT-C polarimetry was usually performed on a 
raster with step size of one array pixel, so that the central map pixel
of the resulting 
map was seen by all 4 pixels.