Proper-motion measurements from HGCA in R.A. and decl. for 12 Psc (top) and HD 159062 (bottom). Three measurements are available: the instantaneous proper motion from Hipparcos, a similar measurement from Gaia DR2, and the scaled positional difference between the two missions (see Brandt 2018 for details). Both 12 Psc and HD 159062 show clear changes in acceleration from 1991 to 2015; the slope of these proper-motion measurements represents the astrometric acceleration.