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This paper investigates the characteristics and the metrological limits of the calibration of spring type gravimeters by using a cylindrical test mass moved vertically around the gravimeter by a lifting device operated in the Mátyáshegy Observatory. The movement of the 3100 kg iron mass generates a sinusoid-like calibrating signal having a peak-to-peak amplitude of 1102 nm s −2 . The careful determination of the geometrical and physical parameters of the test mass combined with the analytical modeling of its gravitational effect and the related uncertainties provides an accuracy of 3 nm s −2 in absolute sense. The overall accuracy, however, is influenced by several other instrumental and environmental factors which are investigated in detail. The conclusions are based on more than 400 experiments with 5 LCR G instruments. As a unique case a Scintrex CG-5 instrument was also involved in the tests what is probably the very first moving mass calibration of this type of gravimeters.Two processing methods, Max-Min and Full-Fit, based on L2 norm adjustment of the observations were developed and applied to obtain instrumental scale factor and other related parameters.The results show that the observations corrected for the disturbing effects still contain a systematic constituent with amplitude of (10-20) nm s −2 regardless which LCR instrument was calibrated. It resembles the second time derivative of the calibrating signal that may indicate the non-uniform elastic response of the spring sensors to the rate of gravity change. Due to the problems mentioned above the overall dispersion of the resultant random and nonrandom residuals of the calibration observations provided by Full-Fit method are typically 10 nm s −2 . The a posteriori standard deviations of the individual scale factors provide, however, measurement accuracy of 2 nm s −2 .

Digital Zenith Camera Systems (DZCS) are dedicated astronomical-geodetic measurement systems for the observation of the direction of the plumb line. A DZCS key component is a pair of tilt meters for the determination of the instrumental tilt with respect to the plumb line.Highest accuracy (i.e., 0.1 arc-seconds or better) is achieved in practice through observation with precision tilt meters in opposite faces (180° instrumental rotation), and application of rigorous tilt reduction models. A novel concept proposes the development of a hexapod (Stewart platform)-based DZCS. However, hexapod-based total rotations are limited to about 30° to 60° in azimuth (equivalent to ±15° to ±30° yaw rotation), which raises the question of the impact of the rotation angle between the two faces on the accuracy of the tilt measurement. The goal of the present study is the investigation of the expected accuracy of tilt measurements to be carried out on future hexapod-based DZCS, with special focus placed on the role of the limited rotation angle. A Monte-Carlo simulation study is carried out in order to derive accuracy estimates for the tilt determination as a function of several input parameters, and the results are validated against analytical error propagation. As main result of the study, limitation of the instrumental rotation to 60° (30°) deteriorates the tilt accuracy by a factor of about 2 (4) compared to a 180° rotation between the faces. Nonetheless, a tilt accuracy at the 0.1 arc-second level is expected when the rotation is at least 45°, and 0.05 arcsecond (about 0.25 microradian) accurate tilt meters are deployed. As such, a hexapod-based DZCS can be expected to allow sufficiently accurate determination of the instrumental tilt.This provides supporting evidence for the feasibility of such a novel instrumentation. The outcomes of our study are not only relevant to the field of DZCS, but also to all other types of instruments where the instrumental tilt must be corrected. Examples include electronic theodolites or total stations, gravity meters, and other hexapod-based telescopes.