  Published high-resolution rotation-vibration transitions of \spec{h212c16o},
the principal isotopologue of methanal, are analyzed using the MARVEL (Measured
Active Rotation-Vibration Energy Levels) procedure. The literature results are
augmented by new, high-accuracy measurements of pure rotational transitions
within the ground, $\nu_3$, $\nu_4$, and $\nu_6$ vibrational states. Of the
\nbNonRedTr\ non-redundant transitions processed, which come from \nbSr\
sources including the present work, \nbValTr\ could be validated, providing
\nbEl\ empirical energy levels of \spec{h212c16o}\ with statistically
well-defined uncertainties. All the empirical rotational-vibrational energy
levels determined are used to improve the accuracy of ExoMol's AYTY line list
for hot formaldehyde. The complete list of collated experimental transitions,
the empirical energy levels determined, as well as the extended and improved
line list are provided as Supplementary Material.
