sfbox draws a boxed baloon-style label, which is useful for annotating graphics.
The following example from sep/avo/imp annotates several reflectors on a seismic section:
sfbox has a large number of parameters to control the box appearance. The most important are: label= for the text on the label, x0= and y0 for the position of the pointer tip (in Vplot coordinates), xt= and yt= for the relative shift of the label with respect to the pointer tip.
The following example from tccs/timelapse/duri uses xt=0 and yt=0 to hide the pointer under the label.
Selecting proper parameters for the location of the label can be tricky. The task is made interactive by the vpannotate script. vpannotate takes a Vplot file as an input and adds an annotation to it. It can do it in the batch mode (when used with batch=y) or in an interactive mode (when used with batch=n). In the later case, the selected parameters are saved in a text file, which can be used as a parameter file for sfbox (or, alternatively, for vpannotate batch=y).