When powered, the Vessel Monitoring Unit (VMU) constantly records data to its internal memory.

The data is compacted into one hour packets.

When the VMU has an internet connection it will upload new data packets to the remote server every hour, or whenever it finds a new internet connection.

Data from the current hour will not be uploaded until the packet has been compiled at the start of the next hour.

In the VMU settings, you can select whether to upload new or old data first, and how many days in the past to synchronise.