Not sure if this app can do stuff like cross multiplication or run the same operations on both calculators. But this app reminded of something similar. There

Not sure if this app can do stuff like cross multiplication or run the same operations on both calculators. But this app reminded of something similar. There is an old school double mechanical pinwheel calculator: https://www.youtube.com/watch?v=qnlzKCFP0sU https://www.youtube.com/watch?v=qnlzKCFP0sU It was probably mostly used for coordinate calculations. I own one of those brunsvigas (the single stage one) and it is fascinating what these things can do. A mechanical calculator with enough didits can solve cross multiplication rather easily.