How to determine current GPU clock speed?

The r304 developer NVAPI wants us to migrate to NvAPI_GPU_GetPstates20(), and marks GetPstatesInfoEx as deprecated. However, it is not obvious to me how to determine the current clock speed when the clock type is PSTATE20_CLOCK_TYPE_RANGE.

I am using a GTX 670 with 310 drivers.

My assumption is I take maxFreq_kHz and add freqDelta_kHz to it. However, I freqDelta_kHz is always zero. If I use the MSI Afterburner app, I see clock speeds near the maxFreq_kHz, but it changes over time when I play the Heaven DX11 benchmark. I never see any of the results from GetPstates20() change. If I want to report current GPU clock speeds, is there something else I should do?