Report System clock accuracy in UniStream: Hardware Posted June 16, 2015 Hi, The RTC error can be of 5 sec each couple of weeks. The allowed drift is up tp 24 sec/month on a 25*C enviorment. There is no direct way to automaticaly change the DST on the PLC via ladder logic. Is the PLC connected to a network with acces to internet? If it does, you can download from the next link examples for UniLogic. http://www.unitronics.com/Downloads/Support/UniLogic/UniLogic%20Example%20Projects.zip there you will find, under \Communications\Protocol a folder called RFC 1305 using message composer. This example will show you how to to a logic on the UniStream so you can update the RTC via internet time server. I hope this helps.