The detector provides an assessment of how likely it is that all or part of the document was written by ChatGPT. Given a sufficient amount of text, the method is said to be 99.9 percent effective.

That means given 100 pieces of text and asked if they are made by ChatGPT or not, it gets one of them wrong. Allegedly, that is, and with the caveat of “sufficient amount of text”, whatever that means.