Master Value vs Local Value (phpinfo)

Can anyone explain to me the significance of master and local values as displayed in php_info? Recently I've tried to increase the php3 memory limit with the php3_memory_limit directive under apache and it does not appear to have an effect. However, php_info does show the increased value under the local value column. The master value remains at the php default. (Around 8.5m) I'm not sure if the memory limit I'm running into is the fault of PHP or Apache, but I am trying to narrow it down. Is it possible that the master value is a limit which can not be exceeded by a local value? or would master/local values be more appropriately termed "default" and "current" respectively? Thanks, Bryan Ingam