Seen this with digital calipers in the past, but this time with a digital tread depth caliper. I like the use of magnets to hold it onto the equipment, and one to help push/pull the measurement rod. I looked on ebay and the cheapest one I saw that would do this mod was $5. Where you can get a 6″ caliper for $5 too. So…not sure which route I would go here. This one looks much cleaner thought.