OpManager CPU, Disk and Memory Utilization Percentage

OpManager CPU, Disk and Memory Utilization Percentage

Hi,
 
How are these performances (CPU, Memory and Disk) being measured in percentage?
 
For example, server1 has drives C & E, how does OpManager come up with a 92% disk utilization? This is for the total disk capacity of server1.
 
 
 
Thanks.

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