This table lists ratios of rest masses of certain particles, where $m_\alpha$ is the alpha particle mass, $m_{\rm u}$ the atomic mass constant, $m_{\rm d}$ the deuteron mass, $m_{\rm e}$ the electron mass (the atomic unit of mass), $m_{\rm h}$ the helion mass, $m_\mu$ the muon mass, $m_{\rm n}$ the neutron mass, $m_{\rm p}$ the proton mass, $m_\tau$ the tau mass, $m_{\rm t}$ the triton mass, $m_{\rm W}$ the W boson mass, and $m_{\rm Z}$ the Z boson mass. The measurements and their uncertainties are given in the format of
[2].