This plot monitors the signal-to-noise ratio (SNR) generated by the halogen lamp in ZIMPOL polarimetry. 
Only the polarimetric direction = zero and cycle  = odd signal is monitored. 
The following setups are covered:

<ul>
<li> V filter,   DIT, NDIT = 4.0, 10
<li> N_R filter, DIT, NDIT = 2.0, 20
<li> N_I filter, DIT, NDIT = 2.0, 40
</ul>
The plot contains four boxes, which shows the signal-to-noise ratio
for both read modes (SlowPolarimetry and Fastpolarimetry) and for both
detectors.