With the large ring laser gyros for the geosciences, we enter the extreme high resolution regime of rotation sensing, observing rotation rates of less than 1 picoradian/s. This requires us to look closely at all potential noise sources in the ring laser itself, as well as in the data acquisition process. Our ring laser measurements for space geodesy are also based on ancillary sensors, such as high resolution tiltmeters, ambient pressure sensors, thermometers and an optical frequency comb for the stabilization of the laser frequency. This chapter discusses the required performance of the detection system together with the performance of the ancillary sensors. We also have to examine the reliability of our numerical algorithms, like frequency estimators, both in the time and frequency domains. With everything included and tested, observations of polar motion, solid Earth tides, ocean loading and the Chandler motion are now possible.