Spectrum uses the following formula to calculate memory utilization for devices that support the UC Davis mib:
((memTotalReal - (memAvailreal + memCached + memBuffer)) / memTotalReal) * 100
memAvailReal attribute id 0x3d00ae
memTotalReal attribute id 0x3d00ad
memCached attribute id 0x3d00b7
memBuffer attribute id 0x3d00b6
These attributes exist on the UCDavisSNMPApp model associated with the device model.