What is an on-line measurement? What is an off-line measurement? See it used here: < In the table giving the different strategies to control growth in a fed-batch culture, one finds, for example: " _on-line_ measurement of glucose". What does it mean? Is there an _off-line_ meassurement? What does it mean?

On-line means that's it's generally continuous, or constantly taking the measure, through a tube connecting the batch.

Offline is used for things that are taken out of the reactor, or removed from the process.

Thus it's "on" or "off" the system depending on whether it's contained within the normal piping/fludics of the system: "On" is in the system, "Off" is out of the system.