Get runtime CPU & memory usage for a running VM

For something that seems so easy, I'm having a hard time figuring this out.

All I want to do is get the current CPU and memory usage of a running VM, but I can't seem to get the information.  I have a simple script that does the following:

var maxCpu = vm.runtime.maxCpuUsage;

var maxMem = vm.runtime.maxMemoryUsage;

var curCpu = vm.summary.quickStats.overallCpuUsage;

var curMem = vm.summary.quickStats.guestMemoryUsage;

System.log("max cpu  = "+maxCpu);

System.log("max mem  = "+maxMem);

System.log("cur cpu  = "+curCpu);

System.log("cur mem  = "+curMem);

var cpuUsage = (curCpu * 100.0) / maxCpu;

var memUsage = (curMem * 100.0) / maxMem;

System.log("cpu usg  = "+cpuUsage);

System.log("mem usg  = "+memUsage);

The "vm" is the VcVirtualMachine object which is an input variable.  VMtools is running on the VM.  When I run the script and select a VM, the cpuUsage shows "0" while the memUsage shows "10" for a particular VM.  I then log into the VM and run "stress" to stress the CPU and/or memory.  I then run the orchestrator script again and the values for cpuUsage and memUsage remain unchanged.  Even if I let the VM stress for several minutes and try running the orchestrator script above, the values still remain unchanged.  I can see the CPU and memory being stressed in the vSphere client so I know the "stress" program is running correctly.  In fact vSphere shows a CPU and memory alarm for the VM after a while, but still I get the same values when I run the script above.

Anyone know what is happening and can give me a solution so I can get the actual runtime values for the CPU and memory usage of a VM in orchestrator?  Much appreciated.