While a lot of analog measurement tools have been replaced by digital ones, Gauge Blocks are still often used as the de facto reference(Though CMM machines[1] are becoming more and more common).

You have a 'Master Set' of expensive Gauge Blocks that you use as a definite reference. Stacks of which can be combined with various tools for various purposes. https://i.ytimg.com/vi/2d-hGd_kYLc/maxresdefault.jpg https://images-na.ssl-images-amazon.com/images/I/61RhwssKaBL... https://i.ytimg.com/vi/n572qMo3g0A/maxresdefault.jpg

The 1 Inch block always seems to go missing.

[1] https://en.wikipedia.org/wiki/Coordinate-measuring_machine