As described in this video, so that we have a reference standard for as close to perfect a right angle as we can for our expanding metrology…department?
Here’s the British Standards for said instrument:
Here is the lump of specific type of cast iron that I plan to turn into said square.
That is beautiful, I don’t know if our metal lathe is accurate enought to make a refference square I would test that a lot before trying to work on the rest of it