It's neat to see how important that key is to your dad. I'm glad your dad is home from the ICU now.
When he was a banker, did they use machines to count bank notes or was it done by hand? When I worked in retail, we used a machine that weighed the bills. We used at th end of every shift to count the money in our till.
They always used to count by hand and even today he remembers that trick and counts so fast, I could never do that.
Impressive! Perhaps you could take some videos of him counting by hand. Could be a precious memory in the future.