You could make a case(ha) for both being comparators vs absolute measuring instruments.That is until they're calibrated against an appropriate standard......
Slight tangent for some lite reading..... look up Long Island indicators and also Mahr metrology. Once on their respective sites,look for tech articles.Keep on point,how can this article or method make your handloading "easier" WRT,all the measuring/comparing that's being carried out. It's like climbing a mountain,the further up you get,quite frequently the steeper.So if you read a book or series of papers and only get one tip....... well,you're that much closer.