Hello,
It depends.
First, let us talk about the width/height. These are entirely governed by the size of the screen and keyboard. So, the more keys, and the more useable these keys are; and the larger the screen, the larger the calculator.
Depending on the specifics of the mechanical on these 2, you will need to add more or less some space around them to hold them in place.
So, this entirely up to you to pick the dimentions that you want based on what you can tolerate on these 2 components.
A classic HP rotate/click keyboard, due to it's mechanical does require more space around than other types of keyboards. The smallest keyboard would be the type of tactiles keyboards that you found in the 80's (http://www.emmella.fr/collection/SHARP_EL_9000_001.jpg , http://www.lexique-informatique.com/T/TO7.html ). Unfortunately, they suck. Then you have the typical membrane keyboards. You know the ones that feel like rubber... etc...
For the Thickness, you have a couple of factors there:
Thickness of the LCD. Unfortunately, because we are a company that needs to design products tested for robustness, and that need to survive a kid's thrown backpack, or a 1m drop on concrete floor, we have to stenghten the LCD. so behind the LCD, you will find an aluminium plate and some padding. This adds close to 2mm to the thinkess of the machine.
Also, because of the HP rotate and click keyboad, we also need to add quite some depth to the machine. first for the height of the keys, then for the travel and then for the thickness of the PCB behind in order for it to be stiff enough not to bow when the keys are pressed.
The last item in this stack is of course the battery. AAA are close to 1cm in diameter. in Prime, we decided to put a rechargeable battery that the user can change. These are thicker than Li-Poly AND require a battery door which itself takes some thickness.
Also, smaller batteries have less power and would not last as long...
If you look at prime, you get a good example of what you can get within these constraints.
So, as a summary, if you want a small calcualtor you will need to:
- Compromise on the size of the keyboard
- Use a keyboard with no tactile feedback
- Potentially reduce your battery life and changeability
- Reduce the product resistance to shocks
But let us say that you had the money to do it and did not care about these items, you could design a calculator with a metal structure ($, but thinner than plastic), a thin unprotected screen, a li-poly battery and a thin keyboard) and probably get to a thinkness in the 3.5-4.5mm range.
Cyrille, Musing
