Its weirdly quite interesting. I have done a few counts, years ago. When young, I worked in a bank, like when customers came in and you had to count bundles of bank notes, accurately. So every election, all the banks were asked for their staff to be used as counters. Got paid ok as well.
So you get a box of slips, sort them into the different piles, then count em into 100 blocks, all the time with a party rep opposite you watching with a beady eye. And as the piles mount up at the top desk, the tension becomes palpable.