I am using Binary because, this project started out very basic. I honestly just watched a video on how memory was stored and wanted to use it on something basic, like button presses to a calculator. Making a Calculator also enabled me to prototype through a game that I could get some "hands on" learning done, which for me is great (also free). Most of these Calculators had Binary switches for inputs though and I was not satisfied with that, especially when the inspiration to the project was saving a button press to a constant "on". It quickly spiraled into an awesome learning process though, much further than the original idea I wanted to explore and I'm very happy to have done so this away. The first Calculator I made (in game) only added to 15, (not using the carry out of the last adder) so I took the same principals of the small Calculator and expanded off of it.
Was this the best or even correct way to go about this? Maybe not, but that isn't the point. The point was to learn and honestly, I enjoy it even more if it was unorthodox. It may not be the most effective, cost efficient, fast or powerful way, but I this did myself. There was no step by step guild. I've needed help on a few topics but I have never asked for direct help (Where do I plug this in? What did I do wrong? Do this for me.). Only "how is this gone about"s. If I wanted to have this done with a micro controller, or some fancier chip I could also have just went down to the dollar store and picked up myself a Calculator there, or at least picked up some Calculating chips that had most of the work cut out for me already but I would have learned much less. My point here is that this was a project to learn basic information off of. Maybe it's not done like this anymore. Maybe it's outdated information that isn't so helpful today. Maybe I didn't follow the best path for executing this idea. But none of that matters. It sparked my interest in the subject, I've learned plenty of things that are still useful today and it has me thinking of other projects to do later on. You learn from the problems you encounter.
So if you are wondering "Why Binary and BCD?" to understand what parameters I could change to remedy the problems I am working under, there you go. But if you are asking why did I do this such an old school, or "dumb" way, I did it to learn.