A down-article indicator (10) which automatically adjusts for the height difference of articles, such as bottles (90), when article size is changed for a new run on a machine (96) conveying articles. A pivotably mounted height sensing arm (20), located on one lane of the machine, downstream from an array of freely pivoting detecting arms (40), is connected by an adjustable mechanical linkage (70) to a pivoting bracket (62) holding a retro-reflective photo eye (61) in proper location with respect to the detecting arms so that the detecting arms do not break a light beam from the photo eye during normal operation. A non-upright article (92) will cause a detecting arm to pivot and break the light beam to stop the machine. As a new group of articles having a different height moves into the down-article indicating station, the height sensing arm automatically moves the photo eye to its proper location for the new height articles. The machine has a 'prime' mode which overrides a stop signal which may be sent by the photo eye while the transition between groups of articles passes through the machine.