The Ysz--Yx Scaling Relation as Determined from Planck and Chandra
  SZ clusters surveys like Planck, the South Pole Telescope, and the Atacama
Cosmology Telescope, will soon be publishing several hundred SZ-selected
systems. The key ingredient required to transport the mass calibration from
current X-ray selected cluster samples to these SZ systems is the Ysz--Yx
scaling relation. We constrain the amplitude, slope, and scatter of the Ysz--Yx
scaling relation using SZ data from Planck, and X-ray data from Chandra. We
find a best fit amplitude of \ln (D_A^2\Ysz/CY_X) = -0.202 \pm 0.024 at the
pivot point CY_X=8\times 10^{-5} Mpc^2. This corresponds to a Ysz/Yx-ratio of
0.82\pm 0.024, in good agreement with X-ray expectations after including the
effects of gas clumping. The slope of the relation is \alpha=0.916\pm 0.032,
consistent with unity at \approx 2.3\sigma. We are unable to detect intrinsic
scatter, and find no evidence that the scaling relation depends on cluster
dynamical state.
