Procure a KIM Uno programmable calculator.
Download all the files at http://obsolescence.wixsite.com/obsolescence/kim-uno-details and make your own or order a kit.
Follow the instructions on the image below under the "To enter:" section to get the program into EEPROM at position $0500. This is a 1 time only step. After that, to use the machine see the "To run:" section.
To use, move the rotors to the desired starting position and type a sequence of numbers. Write down the sequence of numbers shown in the last digit on the right.
To decrypt, move the rotors back to the same starting position used to encrypt and type the encrypted sequence of numbers. The decrypted numbers will be shown on the last digit on the right.