This unit installs in moments with the included hardware and rides underneath Dillon's audible primer sensor.  When that unit goes off, PrimerSense® will also be enabled and it stops the machine at the end of the stroke.  You will then see a note on the tablet to refill your primer tube.  A must-have for people that want full protection from running out of primers which can ruin your whole reloading session.  Covered under the Mark 7® exclusive warranty.