Figure 12 shows the deviation from

Figure 12 shows the deviation from the best-fit sphere, before and after applying corrections based on the reference DMIs. The rms deviation is 1.4 µm with no DMI correction, and 0.75 µm after the DMI correction. An optical interferometer measurement was made at about the same time as the Laser Tracker Plus measurement. The optical data shows that the mirror surface has about 50 nm rms astigmatism (which will be corrected in operation, along with other low-order aberrations, by the adjustable support) and 40 nm rms in other figure error. The 0.75 µm deviation of the corrected tracker data reflects the accuracy of the Laser Tracker Plus system in this geometry.