Good...

good luck with the calculator. will you use binary for your calculator?

Here is an example of one that doesn't use binary (on that I made)

Then doing a decimal calculator may be too complicated. (I generally don't like using WIFI, but it is sometimes necessary)

well, due to the inevitable errors a person might make, about a week or more. It could have taken a lot less, but I had to experiment, and it was my first binary calculator (only) and I was in a constant need of more information. The bin-dec took a long time to understand. If you need any explaining, ask as It will be frustrating for you if you don't understand something.
essentially it is made of the dec-bin, bin adder, bin-dec. It is a bit simple, but the difficult part seemed to be stopping sparks from going where they were not supposed to go.