It is occasionally useful to measure the center position and peak value of a bright arc lamp line in an LRS2 image. Below I show how I would do this after I pull over and unpack the test data tarball.

To grab over and run the image:
% cp ../images/20181115T044859.1_056RL_cmp.fits .
% ds9_profiles 20181115T044859.1_056RL_cmp.fits default default none N 

A portion of the LRS2 Hg arc lamp image viewwd with ds9_profiles. I have drawn a recatngular region with the long axis of the box region placed along a bright spcrtal line. Since the long axis is along the column direction, the marginal distribution will be computed using column-averaging.

Using the box region drawn in the previous figure, a marginal distribution of the LRS2 line flux is computed with column averaging. A set of points near the peak of the distribution was selected interactively (using the using the table_xy_boxclean) and a simple parabolic curve was fit to the data points. This can be used to estimate the center position and peak flux level in the line. Note that this is not meant to be a formal model of the line flux, which would require formal background subtraction. Rather, this sort or exercise is meant to suit a variety of practical HET needs like addressing flux changes due to exposure time changes in the cal script, adverse temperature affects on the red/blue light guides in the cals system, the interodution of a new filter in the optical system, etc....