How is the number of iterations affect the error of calibrateCamera?

Im using, python 3.10, opencv-python

Im doing a stereo calibration. The number of Iterations influences hard my calibration error. Im curious how both interact? If Í set the iterations to < 5 the error drops to ~0.5. When I set the error to >30 the error settles somewhere at ~1.8. Unfortunately the error keeps rising with number of iterations increasing.
The accuracy is barely doing nothing.

How is this working? Which one is the correct error, obviously it cant be the lower one.
thank you for your help!