Introduction
A North American Comparison of Absolute Gravimeters (NACAG18) took place at the Table Mountain Geophysical Observatory (TMGO) near Boulder, Colorado between September 18 and September 21, 2018. Dr. Derek van Westrum of NOAA-NGS, Boulder, Colorado served as the site host and coordinator. While not affiliated with the Consultative Committee on Mass and Related Quantities (CCM), the 2018 comparison was organized following the procedures of the 2016 comparison at TMGO: SIM.M.G-K1, and the technical protocol (again, based on the 2016 comparison) was approved by all participants. The list of participants and a description of the site (including vertical gravity gradients, observed tidal parameters, and superconducting gravimeter signal observed during the comparison) are presented, followed by a discussion of the analysis. The results of the data analysis, and the degrees of equivalence (DoE) of the gravimeters are also presented. For the final solution of the Reference Values (RVs), the contributions of absolute gravity data inconsistent at the 95% confidence level are investigated. Overall, the results and uncertainties indicate an excellent agreement between the gravimeters, with a standard deviation of the gravimeters’ biases better than 1.4 µGal when all instruments are included, and 0.4 µGal when an outlier is removed.