While microelectronics are now the standard for computing, it's amazing to look back at the world of "macroscopic mechanical" computing.

This is a National Cash Register "Class 51" mechanical register built some time in the 1960s:

It took a lot of ingenuity to design a mechanism that could perform the simple functions required by a cash register for a super market. The "Class 6000" was the most complex register that National made and I was very fascinated by watching them in operation at the "Humpty Dumpty" super market in the 1960s.

On one occasion, I was able to see the service man working on one of them and he told me about that the parts were made from heat treated high strength steel to eliminate wear from the 1000s of operations every day. A skilled grocery clerk could perform one operation every second and that could create the potential for a lot of wear and tear on the mechanism.

 

I once (years ago) bought a second hand teletypewirter and made up a 20ma driver to use it as a printer for a PC. Now that was one complicated bit of mechanics. It actually had a reader and punch for paper tape attached. I removed the punch and fitted switches to manually punch paper tape to use in a Eprom programmer. Fun days!

 

It took a lot of ingenuity to design a mechanism that could perform the simple functions required by a cash register

Why not go back in time to the origin of the mechanical computer? The Antikythera Mechanism - https://en.wikipedia.org/wiki/Antikythera_mechanism There were others that were reported back in the time of it but have never been found.

 

Before transistors came out, it seems like cash registers could have used some kind of miniature relay logic (or a combination of relay and mechanical logic) to perform the simple arithmetic functions used in ordinary sales transactions.

The numerical display could have used "Nixie" tubes instead of those rotating dials. However, I believe that National's last fully mechanical register (the NCR "Class 3") remained in production until the mid 60s before it was replaced by all electronic.


It would make a nice science fiction movie for today's engineers and technicians to go back in time and invent a replacement for what is now considered dinosaur technology. I recall there was an episode of the Twilight Zone where someone did this and everyone though he was nutty as a fruit cake.