Keck astrometric measurements as a function of time for all HR 8799 planets. We use the same color scheme throughout to represent each planet: HR 8799b = blue, HR 8799c = red, HR 8799d = green, and HR 8799e = orange. Overplotted are polynomial fits to the data used to determine whether acceleration was detected (Lu et al. 2009). Statistically significant curvature is detected with Keck data only for HR 8799b and e, but has not yet been detected for HR 8799c and d. We anticipate that with continued monitoring and similar error bars, we will detect acceleration using Keck data in 2016 for HR 8799c and d.