The difference between the first and the second input raw biases (in
ADU) is computed. The population standard deviation of the pixel
values of this difference, divided by the square root of 2, is taken
as the RON. Details
can be found in the <a href="http://www.eso.org/observing/dfo/quality/FORS2/qc/bias_qc1.html">plot tutorial</a>.

</font><p><font size="2">
<i>DB Name: fors2_bias <br>
TPL.ID: img_cal_bias <br>
Fits header keyword: QC.RON <br>
QC1 DB parameter: RON_r
</p></i>