> Typically made of granite, surface plates act as a datum, or the basis upon which precise measurements and movements can be made. That's cool! My father was

> Typically made of granite, surface plates act as a datum, or the basis upon which precise measurements and movements can be made. That's cool! My father was an electronic engineer and one of his projects was quite a compact device (as big as 2 decks of cards) that was able, IIRC, to detect a slope of a few microns over a meter, and to take multiple measurements to make a 3d model of the surface. This was paid for by a company [1] that made big slabs of granite, which I reckon must have been these datums referenced in the article. This was almost 20 years ago, and I was in my teenage years at the time. I had built the C# interface to download the data from the device, but I never understood or even though about the purpose of the whole endeavour until this article. 1: https://www.microplan-group.com/en/ https://www.microplan-group.com/en/ EDIT: it might have been a C interface coupled with Gtk, not C#. In retrospect, neither was a very smart or stable choice 20 years ago.