The manufacturer says: "The Standard Horizon ST-20 and ST-20R Offset Receding Stackers offer precise, clean offset or straight stacking. The ST-20R performs offset stacking from the rear of a VAC-100 Collator. The ST-20 has a 13" stack height and a 20-second return time after unloading. An automatic start feature begins system collation immediately after the dolly is raised to the home position."
Please see the complementary Standard Horizon Stitcher/Face Trimmer and Collators, also featured here.