Note how the meter measures actual energy delivered and is insensitive to the power factor of the load. Also clever is how insensitive the design is to attempts to perturb it with, for example, external permanent magnets.
Really amazing that disc can be rotated accurately year upon year with no maintenance.
That is the most fascinating 29 minutes & 58 seconds I have spent in a long time! So much subtlety and knowledge compressed into a piece of equipment most of us never think about. And it was invented over 150 years ago!
Thank you for that link, Mr. W.