============== B ==============

Finally, if the response contains neither header, TTL is calculated based on the age of the content on the origin.
For more information on TTL calculation, please see Time To Live (TTL).

Content Delivery calculates the TTL by determining the elapsed time since the object was modified, and multiplying by a conversion ratio. The default conversion ratio is 20%, and there is also a default maximum freshness check interval of 72 hours. Examples:

============== B ==============

During a freshness check, object B is determined to have been modified 500 hours ago.
Multiplying 500 hours by 20% yields a TTL of 100 hours.
However, this exceeds the maximum of 72 hours.
This means that Content Delivery wont check the object for freshness during the next 72 hours.