Relative astrometric uncertainties, including alignment (filled black points) and centroiding (unfilled red squares) uncertainties as a function of epoch for speckle data from 1995 to 2005 and central 10'' AO data from 2004 to 2011. The median uncertainty of the young stars is reported for each epoch. Alignment errors are minimized near the reference epoch, 2006 June, and increase with time away from this epoch (see Section 3.1.3). All epochs with σ _aln > 0.5 mas are from speckle imaging, where the higher uncertainties are a result of very few reference stars as compared to AO data. The additive errors for speckle and AO are shown as dashed lines.