I wrote an app to use PCSU200.dll - this app will read waveform data from the scope, and calculate the frequency and RMS values.
So here is a trimmed down version of my app, in case someone wants the code to use as a basis for their own project.
My testing suggests that the results are pretty accurate, the frequency is always spot on, the voltage tends to vary by about 30 - 50mV or so, but is consistent so can be pretty reliable.
The Microsoft Visual Studio Express (2013) project for this can be downloaded here.
There are no restrictions on the usage of this code.
NOTE: For this to work properly, both PcLab200.exe and PCSU200.DLL must be in the path or you can copy them to the same folder as the .exe for this program.
Any suggestions for code improvements are welcome!
I hope this helps someone.