Apache Reference: mod_proxy, CacheLastModifiedFactor
Factor Used to Estimate Expires from Last Modified HTTP Field
Syntax: CacheLastModifiedFactor A
Example: CacheLastModifiedFactor 0.5
Since: Apache 1.1
This directive sets the factor that is used to estimate the Expires date from a date of the Last-Modified header field. If the origin HTTP server did not supply an expiration date for the document, then mod_==proxy estimates one using the following formula: expiry-period = time-since-last-modification * factor. For example, if the document was last modified 10 hours ago, and factor is 0.1, then the expiry period will be set to 10 * 0.1 = 1 hour. If the expiry period exceeds that set by CacheMaxExpire, then the latter takes precedence.