I do think that the ability to do calculations in your head or with pen and paper is something you get good at by practicing it. Obviously if you don't do much math at all it doesn't matter whether you have access to calculators or not. But if you do math and depend on a calculator, then I think you will be less good at doing calculations by hand (and less good at analyzing and thinking about the size of numbers) than if you hadn't used a calculator as much. I'm sure there has been research about this, though, and I am open to changing my mind if the research results say otherwise. : )

Slide rules made you aware of powers of ten and the size of numbers in a different way than a calculator, I think, since you have to determine yourself where the decimal point should lie. Not that I want to go back to slide rules. *g*