  Electron emission can be utilised to measure the work function of the
surface. However, the number of significant digits in the values obtained
through thermionic-, field- and photo-emission techniques is typically just two
or three. Here, we show that the number can go up to five when angle-resolved
photoemission spectroscopy (ARPES) is applied. This owes to the capability of
ARPES to detect the slowest photoelectrons that are directed only along the
surface normal. By using a laser-based source, we optimised our setup for the
slow photoelectrons and resolved the slowest-end cutoff of Au(111) with the
sharpness not deteriorated by the bandwidth of light nor by Fermi-Dirac
distribution. The work function was leveled within $\pm$0.4 meV at least from
30 to 90 K and the surface aging was discerned as a meV shift of the work
function. Our study opens the investigations into the fifth significant digit
of the work function.
