RPN Calculator ( Like the old HP calculators )

I wanted a RPN calculator like the old Hewlett Packard ones. So I made my own.

Here's a link to the writeup with instructions for building your own: http://leftcoast.biz/iWeb/Left_Coast/The_calculator.html

A link to it running : https://www.youtube.com/watch?v=s-vngUi7-kw

The touchscreen : https://www.adafruit.com/product/1947
The power system : https://www.adafruit.com/products/1944
The power switch : https://www.adafruit.com/products/805
The battery : https://www.adafruit.com/produ