'What does `CALIB_CHECK_COND` flag of the OpenCV function fisheye::calibrate() do?

In the OpenCV documentation for fisheye::calibrate it says that turning on the flag fisheye::CALIB_CHECK_COND means that "the functions will check validity of condition number", but I have no idea what that means.

Here is the source code for fisheye.cpp.

What does CALIB_CHECK_COND flag exactly do?

This flag is also relevant for this question, but no one seemed to have figured it out.



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