When setting up my EggBot, i do a lot of fiddling with arm height, egg centering, servo up/down position, etc. I used to mount a Sharpie in the holder, and mickey-mouse the measurements while trying to make sure not to mark the egg.
Turns out, using a "dead" Sharpie makes things a lot simpler. I built one by ripping the guts out of a Sharpie, trimming its tip a bit, inserting a 1/4" dowel with toothpick down the body, and clamping the dowel so the toothpick stuck out just the same amount as a Sharpie's ink tip.
If anybody replies to this asking for more details, I'll gladly be more specific. In the meantime, all I can say is that with my work-flow, things are now a lot easier. I can do all the fiddling I need without worrying about marking the egg.