[themccannman]

Buy some cheap calipers that are used for light scribing and hand made parts. Keep the expensive calipers/micrometers with the machines where they are used specifically for measuring part tolerances. Also, most of us are using 6061 aluminum, it will take a while to damage the tip of a steel caliper as long as you aren't trying to cut your part using the ends. When you use marker to pre-mark the surface before etching you barely even have to touch the surface to make your line.