Best edge finder?

[Rickabilly]

I've been using the LED style spring loaded ball on a stick type for ten years now, I get five years battery life without drama, absolutely rock solid reliability, except when one of the employees bent one by crashing it hard in a CNC MC , they use a 10mm ball on the end spring loaded into a ground socket so you can overshoot without damage, to test it for runout simply find an edge and zero then rotate the finder by 180 degrees and retest, they can also be set for depth to set z offsets but they suffer from overshoot unless you are very careful, For Z's I use a 50mm LED Z tool which sits on top of the work and you bring the tool down to it until the light shows, at which point the tool is 50mm above Z surface, too easy, one very important point is that they don't work on non conductive work, but there are ways around this, number one is to use the vise jaws as datums, as you generally know where these are in relation to the work, like touching the work that is.

Rick