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PLC > Edge > MQTT Server > Engine
The timestamp for a tag read from a PLC will be the timestamp assigned by the PLC.
This timestamp will be passed to the Ignition tag and delivered via MQTT Transmission to MQTT Engine.
In general, the Edge is the source of truth for tag timestamps although there are several events that will cause the timestamps to differ across the system:
Time at PLC is older than Transmission or Engine leading to tag change events being ignored as the new event time is before current time for the tag at Engine