I would like to fetch some data from other sites or from a web service, how can I do that?

It is easy to do, but requires some knowledge in JavaScript and HTML. Just add a JavaScript function that fetches the data and stores it into respective fields. If you look at the web page, you see that the form fields are named with the same names as the corresponding spreadsheet cells. You can make the new fields hidden and/or read-only.

How to I set a constant used by the calculator programmatically?

If you have created a calculator, and there are some constants you want to set, for example the current rate, then read the following:

How to initialize values on the server

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