Back in 2018 I designed a type of comparator (and setting master) for compressor valve grooves. Just finished another batch of 10 of them, it went well. Nowadays we wrap the master in paper along with oil in order to prevent rusting. Sending them to the southern states made them rust a fair amount.
Just leaving this here for posterity.
They are a pain in the ass to align well though, I am going to do a mild redesign on the next set. I always say that but we always need them yesterday.