Statistical uncertainty of 2.5 × 10 − 16 for the 199 Hg 1 S 0 − 3 P 0 clock transition against a primary frequency standard

High-resolution spectroscopy has been carried out on the ${}^{199}Hg$ ${}^{1}{S}_{0}\\ensuremath{-}{\\phantom{\\rule{0.16em}{0ex}}}^{3}{P}_{0}$ spin and dipole forbidden transition, where the atoms are confined in a vertical one-dimensional optical lattice trap using light at the magic wavelength. We describe various characteristics of the resulting line spectra and assess the strength of the Lamb-Dicke confinement. Through a series of absolute frequency measurements of the ${}^{199}Hg$ clock transition with respect to the LNE-SYRTE primary frequency standard, recorded over a 3-month period, we demonstrate a statistical fractional uncertainty of $2.5\\ifmmode\\times\\else\\texttimes\\fi{}{10}^{\\ensuremath{-}16}$. We include details relating to the generation of ultraviolet light at three wavelengths necessary for the experiment: 253.7 nm for cooling and detection, 265.6 nm for clock transition probing, and 362.570 nm for lattice trapping, along with further aspects related to the magic wavelength evaluation.