In general, if the device has its own memory then no data loss occurs. Otherwise, data loss does occur for the time that iChart is not running or when the computer is off. Exceptions to this rule include:
A Vaisala WXT520 weather transmitter connected directly to a computer: Closing iChart or the turning off the computer causes data loss.
A YSI sonde connected directly to the computer: If it is logging in Unattended mode, then no data loss occurs. If it is running in Discrete Sample mode, then data is lost .
A NexSens iSIC data logger that is connected to the computer: Data loss only occurs if the “Log in iChart” feature is enabled.