A related tip for burning small, specific areas - use a standard burn card that's white on top and black on the bottom. Slide a sheet of red lighting gel or rubylith over the hole.
Hit the timer and use the white surface to get the card positioned - then slide the gel out of the way with your thumb, watching the image on the card to determine your motions. When you reach the proper number of seconds for your burn, slide the gel back over the hole.
I've found this to be really accurate and saves me from burning a circle around the print as I try to get the hole aligned.
For Lith printing, I often need a flashing mask, a card raised over the print with cutouts. I use the red filter to get this positioned, pull the neg, and flash through diffusion. Works REALLY well to control highlight exposure.