Chu Y, et al. – Researchers comparatively evaluated the spatial calibration process for front–end endoscopy and redefined the accuracy level of a calibrated endoscope by using a calibration tool with improved structural reliability. The outcomes demonstrated that a trade–off for a new minimal time of registration can be reached when the distribution of five fiducial points (FPs) is considered. For in–surgery registration, the data illustrated that the intrinsic registration error is a major cause of performance loss.