Hello (sorry for the late reply).
Well, I did that by html and javascript.
So, you'll need to do some programming if you want something similar.
If you want to look at the code, just go to the page and click with the right mouse button.
If you're on Firefox on the menu that will pop-up there's a "View page source".
Another way is to download the whole page:
windystar.awardspace.com/calcu... on your computer (it also works offline since all the code is within a single document). Then (after you download it), you can open it with a text editor (like notepad) to look at the layout/source code (html tags, javascript, etc).
Now, if you want me to program your own calculator, I might think about a commission (I've not done commissions before, but I guess there's always a first time
)