Putting vertical and horizontal lines on the spectrum

There are times you may wish to guide the eye of your readers to some feature of your spectrum. A vertical line (extending the entire height of the spectrum plot frame) can be put at, say, 56 km/s by typing:

$>\!>$ vert 56

A plot has to be open for this to work. The plot will be redrawn.

In SPECX 6.3 I didn't find any equivalent for horizontal lines, but if you really want to do this, one method that works is to multiply your spectrum by zero number, offset to where you want it vertically, and replot the spectrum. Thus, say:

$>\!>$ mult 0.0; off 2.5; over 1 6

would put a horizontal line on your open plot 2.5 K above zero. This also allows one ready control over both line width and color. SPECX 6.7 includes the baseline command which implements this sequence for you.