I'm often told that people are resistant to change, but I think this isn't entirely true. People are resistant to sudden and dramatic change. Small changes over time often go unnoticed, like the proverbial frog in a pot of boiling water.
You want your first calculator to look a lot like an abacus, but have a few new features which introduce the user to the new capabilities of the new technology and ease them into change.
> People are resistant to sudden and dramatic change. Small changes over time often go unnoticed, like the proverbial frog in a pot of boiling water.
This is true, but the physical calculator interface is so old that it would take decades of careful enhancement and deployment to move its users up to a modern interface. Most of its users just want to multiply large numbers, or add a column. The word processor is a great example of the incremental interface changes you describe though.
You want your first calculator to look a lot like an abacus, but have a few new features which introduce the user to the new capabilities of the new technology and ease them into change.