I'm probably not the only guy who has used the outer edge of the fixed jaw of my calipers as a scribe guide to lay out a line on a Dykem covered surface. Considering what my Mitutoyo Digimatics cost, I decided this was a procedure to be avoided so I made this markout guide. The movable steel bar is set to the desired length with the calipers, locked in place with the lock screw, and its outer edge used to guide the scribe.
This end view shows the implementation of the lock block. The screw pushes it down into a milled recess and the 45 degree angle bears on the slide to clamp it against the bottom and side of the channel in which it slides.
Apologies for the fuzzy picture. I have better cameras now and have developed some modicum of photographic finesse. If you need better photos, alert me and I'll provide them.
I don't do much detailed marking out anymore since equipping the mill with DIs in all three axes. What little I do is to provide gross sanity checks so, if I somehow miss a complete revolution of the DI needle, the markout will highlight my clumsiness.