How can I tell when the configuration was changed on my ProxySG appliance?

Configuration changes are logged logged in "Configuration Change Events" (URL_Path /Eventlog/fetch=0x02000000). 
This information can be found in Sysinfo (https://proxy-ip:8082/sysinfo). 

Please see example below.

Configuration Change Events 
URL_Path /Eventlog/fetch=0x02000000 
2015-06-16 19:42:35+08:00SGT  "Administrator action, user 'admin', from x.x.x.x', Viewed event log"  0 60003:7D   cag_agent.cpp:1467
2015-06-16 19:43:27+08:00SGT  "Administrator action, user 'admin', from x.x.x.x', Downloaded event log"  0 60003:7D   cag_agent.cpp:1467
2015-06-17 11:34:59+08:00SGT  "Config admin at A.B.C.D 'user1', added primary DNS server "x.x.x.x""  0 140002:7D   cli_parse.hpp:268
2015-06-17 13:07:49+08:00SGT  "Config admin at E.F.G.H 'admin', installed new VPM Policy File and VPM XML File"  0 140002:7D   cli_parse.hpp:268
2015-06-17 13:09:06+08:00SGT  "Config admin at E.F.G.H 'admin', installed new VPM Policy File and VPM XML File"  0 140002:7D   cli_parse.hpp:268

For information on the previous date, customer needs to access "Snapshot" part. 
https://proxy-ip:8082/diagnostics/snapshot 
Look at "Snapshot sysinfo:", and choose date, then go to part "Configuration Change Events" in the Snapshot Sysinfo. 

Limitation
- The specifics of policy changes are not detailed here. Just that a user made a change.

-The detailed changes made via VPM are not logged in Eventlog, the only message logged to Eventlog is:

2015-06-17 13:09:06+08:00SGT  "Config admin at E.F.G.H 'admin', installed new VPM Policy File and VPM XML File"  0 140002:7D   cli_parse.hpp:268