SPM Error Estimates

Errors are estimated based on the scatter of multiple measures of the same star.  Typically, a star may have multiple images on the same plate (grating images and offset exposure), both blue- and visual-plate measures, or first- and second-epoch plate measures in the case of the photometric measures, and may also be in the overlap region of adjacent fields.  For stars with only a single measure, (i.e. faint objects near the field centers), we adopt the average estimated error of neighboring stars' images of similar signal-to-noise, generally in another image system.  The plate modeling errors are also folded in to produce the final error estimates.  The figure above shows the errors in V, absolute proper motion, and position as a function of magnitude.