This plot monitors the signal-to-noise ratio of the ZIMPOL imaging master lamp flat. 
The underlying assumption is, that all planes of the raw frame cube are
illuminated with the same number of counts.

The following setups are monitored:

<ul>
<li> V filter,   DIT, NDIT = 4.0, 10 and 8.0, 8
<li> N_R filter, DIT, NDIT = 2.0, 20 and 2.0, 8
<li> N_I filter, DIT, NDIT = 2.0, 40 and 2.0, 8
</ul>