upset by dynamical events. Since the orbital periods of the HR 8799 outer planets span centuries, only small arcs of their motions around the star have been measured in the years since discovery, leaving significant uncertainties in their orbital elements. Early stability calculations indicated departures from a face-on geometry [@fabrycky10], and most analyses have favored orbits with inclinations of 10 to 30$\degr$ [e.g. @currie12; @esposito13; @pueyo15; @wertz17]. A recent analysis of carefully calibrated astrometric monitoring data that minimizes systematic errors generally indicate more highly inclined orbits, specifically $38\degr\pm7\degr$ for the outermost planet b, and no evidence for any measureable departures from coplanarity [@konopacky16]. Astroseismology suggests a higher inclination angle for the star, $\gtrsim40\degr$, as well [@wright11]. These results are all compatible with the disk inclination of $32\fdg8^{+5.6}_{-9.6}$ derived from the combined SMA and ALMA data.

There is some tension between the millimeter result and the lower (and more precise) disk inclination of $26\degr\pm3\degr$ determined from the ellipticity of the outer edge of far-infrared emission in [*Herschel*]{} images [@matthews14]. As noted by @booth16, the discrepancy between millimeter and far-infrared disk inclinations may have a physical origin in size-dependent dust dynamics, or in complexities in disk structure not captured by the simple 