**7. Conclusions**

A new experiment was presented for the determination of the Newtonian constant. It is based on a time and frequency metrology approach consisting in the measurement of the small frequency difference between two freely oscillating pendulums via their time delay rate of change. A system of dense field masses is moved back and forth between the two, alternately increasing one frequency and reducing the other and vice versa. The increase in resolution by averaging is fast in this case because the limiting noise is white delay noise, which yields *σ<sup>y</sup>* (τ) proportional to τ−3/2. This fact is unique among experiments for the determination of *G* and offsets the poor signal size problem allowing to focus the design on accuracy rather than S/N ratio. It remains to be shown that differential stability in the 10−12 region can be obtained with consistency for two similar pendulums of the design which has been sketched here. This seems to be a long shot when considering the absolute stability achieved by the best Shortt clock [13], because it requires an improvement of more than three orders of magnitude with respect to it, at the target few hours (*T*R) averaging time. However, it is not unreasonable to think that two adequately similar pendulums can be realized, and if they are within 100 mm of each other, it can be expected that *g* uniformity may be adequately stable in time to support the assumption. A description of the apparatus and a discussion of pendulum design optimization for this experiment were offered in detail, pointing out problems and possible solutions. Work is in progress on the preparation of the experiment, considering both a free decay solution and pendulum operation with active support of oscillations and amplitude control. It is expected that an accuracy of 10−5 may be obtained for *G* with the proposed approach, limited only by the accuracy of field masses' size and positioning, and that it may be possible in a metrology laboratory to reduce limiting geometrical uncertainties enough to push it into the 10−6 range.
