Earlier quoted context omitted.
Hand counting is how we do it in the U.K. It’s not actually that hard at all, including validation, through simple physical processes (that are incredibly tried and tested!). Write the contents of the vote totals on the outside of the box containing the ballots (total must reconcile to number of ballots placed in), then total all the box totals at the end for a single constituency. Constituencies then report back. We…
There are scaling issues though. The US is 5x the size of the UK. Counting is actually pretty hard and I'm not convinced it scales linearly. I'm also not convinced results are actually back in a day, but rather good estimates are given within a day.
It’s literally an ‘embarrassingly parallel’ problem.
A hundred people can count ten times the ballots that ten people can, and then merge their results.