So, following that logic - how do I determine that "source"? Here's a simplified example: let's say, I live in FL but work for a CA accounting company that does tax returns. Let's say, the company only has offices in CA. I log into my computer, access financial documents stored on company's server in CA, complete all the work on my own computer, and then upload completed tax returns back to company's server. In this case, what is "a source where the services are performed"?
