What is the accuracy of RTC?
Site with controllers using the RTC Crystal Quartz chip (controllers such as the ACX)
What is the accuracy of Real Time Clock?
When the controller is powered down, the battery-backed RTC Chip has an accuracy of +/- 1 minute per month. When powered on, the controllers use the RTC chip as a reference point but keep time in software. Experience has shown an accuracy of 1 – 2 seconds per month when controllers are offline and not re-synched from the Network. Since that is typical and not calculated, a conservative number would be +/- 10 seconds per month. When Online,the accuracy is determined by Cyberstation which can itself be synched to an extremely accurate NST Server. I2 and B3 controllers are re-synched once per hour.
For Sync time in Cyberstation(s) and Server check Sync time in Cyberstation and Server.
For more information see What are the differences between a hardware and a software Real Time Clocks (RTC)?.
For how field controllers keep their own internal time check How do our field controllers keep their own internal time?