I think your calculator project is more interesting than the first two, mainly because it requires you to actually give some more thought into a user’s process in calculating something vs. A typical ux pattern that’s been done a million times. I encourage you to think further and revisit the calculator project; it’s a bit lacking in overall UX considerations. I think you need to ask yourself what users are doing when using a calculator, and let that influence the way you organize and size these buttons. Think about what users do first. Probably type in value A, then an operation, then value B, then hit equals. Equals is always the last button to be hit, so maybe it needs prominence; either in larger sizing or placing it in a more memorable area like the very right corner. This is also why some calculators have a larger equals button, or sometime also a larger zero button. You have to wonder why calculators are designed the way they are and why all buttons aren’t the same.