How I made my own granite surface plate

Hey guys so I’ve been wanting my own reference surface/ flat surface and for the most part I’ve been using a piece of cast iron from my table saw, but when I seen these piece of granite am idea form in my head so use these and this is that process. How I took these piece of granite that where anything but flat and took them to within a couple of hundred microns of absolute flat. Thanks for watching if you enjoy my content consider subscribing.