It is useful to have an independent measurement of the total flux by
means of a standard filter measurement before the actual use of the
polarizers. For the standard filter measurement, where the entrance
wheel is set to ``hole'' position, the bare minimum the for number of
exposure atken through the hole position of the selection wheel,
, may be estimated according to:
The minimum value of
should be larger than 12.
In the example as above (Section 3.1), the recommended value of
15. The hole measurment will also be performed in
raster mode as recommended for the three polarizers (Chapter 2).