Glad you're enjoying it. There's another fun aspect that you might want to play with. It's talked about in the manual a bit. You can bootstrap your program on cards. That's why memory location 00 is set "permanently" to 001. (The simulator does let you change it.) The bootstrap starts with the two cards 002 and 800. They are followed by pairs of cards containing the address and value of what you want to load into memory. Then, to make it jump to the first instruction of your program, the last two cards will be 002 and 8xx where xx is the address of the first instruction. Finally, any input data is put after the 8xx card. I've relocated your program to address 10, used memory locations 5 and 6, and reused the 001 in location 00 for your decrement constant in the cards below. If you start with clear memory, cut and paste this list into the input box, hit reset and hit run, it'll load the program into memory and run it. 002 800 010 005 011 105 012 606 013 700 014 320 015 605 016 206 017 606 018 105 019 813 020 506 021 900 002 810 060 BLS