ashtech DG16 Reference Manual page 68

Figure 3.3. Timing Pulse Characteristics
In order to provide notification to peripheral equipment and software with respect
to time tagging the occurrence of the timing pulse, it is necessary to set the output
of PBN raw data message to match the period of the timing pulse. The GPS time
value contained in the PBN message plus one second is the time that the next
pulse will occur when the default settings are in effect (Figure 3.4). PBN time is
already internally rounded to GPS time, so it is the actual time to which the
navigation 1PPS pulse generation which preceded it (unless that pulse has been
intentionally advanced or retarded). The latency of PBN message output is
normally about 40 milliseconds after the timing pulse event.
Figure 3.4. Relationship of GPS Time in PRN Record to Output of 1PPS
Pulse
48 DG14 and DG16 Board & Sensor Reference Manual