  We report on a preliminary scale determination with gradient-flow techniques
on the $N_f = 2 + 1 + 1$ HISQ ensembles generated by the MILC collaboration.
The ensembles include four lattice spacings, ranging from 0.15 to 0.06 fm, and
both physical and unphysical values of the quark masses. The scales
$\sqrt{t_0}/a$ and $w_0/a$ are computed using Symanzik flow and the cloverleaf
definition of $\langle E \rangle$ on each ensemble. Then both scales and the
meson masses $aM_\pi$ and $aM_K$ are adjusted for mistunings in the charm mass.
Using a combination of continuum chiral perturbation theory and a Taylor series
ansatz in the lattice spacing, the results are simultaneously extrapolated to
the continuum and interpolated to physical quark masses. Our preliminary
results are $\sqrt{t_0} = 0.1422(7)$fm and $w_0 = 0.1732(10)$fm. We also find
the continuum mass-dependence of $w_0$.
