Yes, %S13 is the first scan bit. It will be set to a value of "1" during the first scan and will automatically reset to "0" at the end of scan. This bit is also available for Premium and Quantum CPU's using the Unity OS.
Legacy KB System (APS) Data: RESL199279 V1.0, Originally authored by TVe on 07/02/2009, Last Edited by TVe on 07/02/2009
Related ranges: Unity Pro