DMC-1 Question

I'm not sure of the function of the SI signal circled in red. Can anyone provide me any information on this signal?

Thanks

NOTE: Whenthe car ls on SCA(SeIactiv8 Collective Autornatlc) and level wIIh a Floor, SI should be 24 VdC. When the car norms, SI goes to 0 VDc.
Upon reaching Slowdown distance at the Target Floor (stopping), SI will 90 back to 24 VOC.


page 5-32 (DMC 1 Control System)