I thought I just saw you at Dividend Machines. Glad to see you asking questions on both sides!
The formula stated by the link you provided is one of the ways to determine free cash flow.
I usually prefer to use owners earnings. The formula is operating cash flow before working capital minus the purchase of property plant and equipment. The reason is because some companies may not necessarily have consistent operating cash flow, especially those who are growing its biz may require volatile working capital, thus making it hard to determine its true ops cash flow. That being said, the use of owners earnings must be used with caution as some companies may not necessarily have healthy working capital. Simply said, if the operating cash flow is frequently negative causing the company raising money regularly, you not want to use it.