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An overview of the data transfered is available here: Explanation of volume export data.
When automatic transfer is activated, the tia® Status UI can be user to display volume information, which refers to the aggregated volume data sent to kgs server. Read more here https://kgs-software.atlassian.net/wiki/spaces/DOCUEN/pages/2738061313/tia+Status+User-Interface#Show-volume-measurement.
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Volume measurement is not available with content service kgsstore (accessing legacy storage created by tia® Content Server Classic, for more information see kgsstore ).
Regarding questions or troubleshooting on Volume Measurement, read more here: Volume Measurement - FAQ and Troubleshooting.