You explained what you are setting the plugin to but you never explained **exactly** how you are measuring the output value? Do you have an actual VU meter? Or are you measuring voltage? What *exact* device are you using and what exact level are you looking for? Are you factoring in load impedance corrections?
You want what calibration level? 18dB headroom above 0dbFS = 0VU = +4dBu
dBFS is always peak... from the literal meaning of "full scale" So if you can really measure 0VU on a real VU meter then set the signal generate to use peak--the template was correct. There are no other things to think about (even with VU itself being defined against a V rms reference that does not matter, since here you are using 0VU as the reference measured on a VU meter).
But just calculate the numbers needed if you want to read any other how, or read at a different calibration point to make turning the pot easier... e.g. aim exactly for 2V pp on an oscilloscope.
The calibration instructions could be better in my option. How many places have a VU meter handy vs. a digital multimeter? And which is likely better calibrated/easier to set things to more closely across the channel?. So just work out what to do yourself. And think it through carefully... are you are using a VU meter what impedance is it calibrated for 600 Ohms actual spec definition.. Or... ? Do you want you want to correct for source/load impedance?, ... the 600 ohm VU spec load impedance across the ~50 ohm HD IO Output impedance(thanks BScout
) .. then you can factor in the ~0.7 dB difference if measuring voltages on an effectively infinite impedance volt meter or oscilloscope (make sure any scope is in a high input impedance mode)).