Existing pocket calculators are cheap commodity devices, due to their relative mechanical and electronic simplicity.

Making a reliable rotary control system will increase cost and a certain complexity to the user.

The buttons calculators have are as simple and cheap as it gets.If they are too small, get a bigger calculator. They come in all sizes.

Pep, This brings to mind an image from a commercial (I don't remember what for) ofa guy dialing a computer keyboard.

Though I prefer a knob for any analog setting (for instance volume), it's pretty hard to beat a button for a digit. And as someone who calculates often, I think the ten-key on the computer keyboard is better than my pocket calculator. touchscreen on the phone is worst.

This type of rotary knob is only meant for miniature calculators,it would be too cumbersome to use a keypad built into a watch.

Don't make calculator watches then. Anything that small would be a novelty, pretty well.

Moving parts + small devices = fail

True, moving parts are bound to fail, ever tried to use a watch calculator you will know how cumbersome it is use thetiny keypad. These rotory knobs will make it much easierto operate a mini calculator.