If the dataloggers are connected over some form of serial/PakBus link, they can be synchronized with each other using the ClockReport() and PakBusClock() instructions in the dataloggers. Use the ClockReport() instruction in the master (time) datalogger and the PakBusClock() instruction in the slave dataloggers. The option to broadcast to all can be used (providing no routing is needed), which means that just one packet of information is sent.
The ClockReport() instruction can be used as frequently as desired, although, for practical purposes, once or twice a day should be adequate for most applications. The clock should be set at a time that does not interfere with the timing of dataloggers storing their data.
If the dataloggers are connected over an IP network, use the NetworkTimeProtocol() instruction so that one datalogger acts as the time server.