Monitoring SNMP usage with SNMP

Anyone doing SNMP monitoring on Fortigate devices?

I'm getting different values when reading memory used values with SNMP as opposed reading them from some CLI and GUI.

When reading SNMP OID .1.3.6.1.4.1.12356.101.4.1.4.0 i get:

SNMPv2-SMI::enterprises.12356.101.4.1.4.0 = Gauge32: 81

When using the new 5.6 command 'diagnose hardware sysinfo conserve' cli command i get:

memory conserve mode: off total RAM: 1866 MB memory used: 1329 MB 71% of total RAM

So that's a difference of 10%

When i look at the memory usage in the GUI (Global main dashboard) i also see 71% memory usage.

Then again when using CLI command 'diag sys top-summary' (currently broken in FortiOS 5.6.3!) i get a value of 81% (same as SNMP)

When doing multiple tests i always see a 10% difference.

Tests are performed on FortiOS 5.6.2