The figure shows that for M stars, the APF requires fewer photons in the region to achieve velocity precision comparable to Keck. [Based on the work of Bouchy et al.,13 we expect that for K dwarfs, the relative speed should scale as the “information content” ,14 which is proportional to the ratio of the resolutions, . For HIRES, the “throughput” (the resolving power times the angular size of the slit) is 39,000′′15 and for the APF it is 114,000′′.2 Normally, HIRES was used with the 0.861′′ slit giving a filled aperture resolution of 45k while for the Levy a 1′′ slit is used, so the ratio of the resolutions is 2.5. The Levy demonstrates a larger than expected improvement over HIRES which could be explained by the increased number of lines in the iodine region for M dwarfs. Further investigation is beyond the scope of the current paper, but we plan to include such analysis in a future publication. We note that the excellent seeing at MK means that some data were observed with a much higher effective R, up to 90 k, which may explain the large scatter we see in Fig. 5.] Speed estimates for the APF/Levy, carried out last year,2 show that the telescope and instrument together are approximately slower than Keck/HIRES. Combining these two effects indicates that the APF has essentially the same speed-on-sky as Keck/HIRES for precision RVs of M stars. This is not altogether unexpected, as HIRES was never specifically optimized for precision RV work. The APF’s Levy spectrograph was purpose-built for high precision, RV science and therefore features much higher spectral resolution and finer wavelength sampling than HIRES. Both of these factors, as well as the significantly higher system efficiency of the APF/Levy optical train over that of Keck/HIRES,2 combine to make APF as fast as Keck/HIRES for precision RV work on M dwarfs, at least down to .